The Night of Destiny (Leilatul-Qadr) is an important and blessed night which is, according to the Holy Quran located in the month of Ramadan.
About this question there are several probabilities:
1- What we mean by the multiplicity of the Night of Destiny in one year is that it may fall on the night of the 19th, 21st, and 23rd of the month of Ramadhan..
2- What we mean by the multiplicity of the Night of Destiny may lie in the fact that there was such a night in the Prophet Mohammad’s (s) time and it was repeated after him.
3- What we mean by the multiplicity of the Night of Destiny is that there is a time zone difference in various Muslim cities. This difference in the days of the month of Ramadan in different regions may be the reason for having the Night of Destiny in various times for each city.
In response we should say that what people say is not based on viable facts. We don’t have more than one night of destiny and that is the night when the Holy Quran was brought down and the destiny of people was given shape. God says: “Truly we sent it down on the night of destiny” and not on any other night.
For the second probability it should be mentioned that according to the Verses of the Holy Quran and various traditions the night of destiny is not limited only to the time during the life of the Prophet Mohammad (s), it reoccurs all throughout the years like the ‘feast of the sacrifice’ (Eid Qurban, also known as Eidul-Adha) which is repeated every year. God says:
1- “Therein descend the angels and the Ruh by Allah’s permission with all decrees"
2- “Therein (that night) is decreed every matter of ordainment.”
In these two verses the verb “sent down” and decree both have been used in the present tense and imply continuity.
We have various traditions that the night of destiny is repeated every year. On this night God’s decree for one year is sent down.
For the third possibility it can be said that the time zone difference does not make the night of destiny fall on different nights. If Muslims don’t fail to realize the first night of Ramadan and do their religious duties and keep awake on the nights likely to be the night of destiny, they will certainly be blessed by God even if they have kept awake on the wrong night. It is obvious that some features of this night like the sending down of the angels on God’s apostles only happens on the real night of destiny. It can be understood from the traditions that the day of destiny is as valuable as the night of destiny. However some affairs like the management and the sending down of the angels happens on the night of destiny. God says: angels and the spirit are sent down and they bring the destiny for things on this night.[i]
[i] Surah Qadr, Verse 4
Before giving an answer to this question we should first make an analysis on what the original inquirer meant by the multiplicity of the Night of Destiny (Leilatul-Qadr). Does it mean that all the nights specified in the last ten days of the Month of Ramadan i.e. 19th, 21st and 23rd are the Night of Destiny because there are some special rituals for them? Or is the night of destiny just one of these nights?
Or does it mean that the night of destiny happened only once in the Prophet Mohammad’s (s) time or it happened several times? If the matter of the multiplicity is true did it happen at the time of Prophet Mohammad (s) only or did it also reoccur after him as well?
Is multiplicity due to the time zone difference between different Muslim cities throughout the world? For example the Holy Month of Ramadan begins from Tuesday in one country and from Wednesday in another and as a result there will be differences in the last days of the month in these countries. It is obvious for the former country the 23rd night is one night before the same night in the second country. Therefore the night of destiny can not be one specific night in a year. Hence, they will have their own night of destiny and this makes the various days possible.
To answer the first possibility according to the Holy Quran we should say that the night of destiny is in the Month of Ramadan and it is not more than one night as God says in the Holy Quran: "Truly we sent it down on the night of destiny" and not on the night(s) of destiny. However this night has not been clarified for us in some respects . They say that among these nights; 19th, 21st, or 23rd is one of the nights that we should keep awake throughout all of the night so that we can receive the blessings of it. The reason why three nights have been specified in traditions is only to make it easy for God's servants.
The answer to the second possibility is that the Holy Quran and the progeny of the Prophet believe that The Night of Destiny happened at the time of the Prophet Mohammad (s) and it still happens yearly. We can understand from the verse "Therein the angels and the Ruh are sent down by Allah’s permission with all decrees" that the verb "descend or sent down" is used in the present tense and this implies the continuity of this action.
Also in surah Dukhan, in the sixth verse which is about the night of destiny it is said: “Therein (that night) is decreed every matter of ordainment. as a command from us. Verily We are ever sending the Messengers. In this verse the verb decree used in present tense indicates the continuity in the Arabic language.
The traditions from the Progeny of the Prophet also emphasize this fact.
Imam Jawad (a) said: Imam Ali (a) told Abbas: "The night of destiny happens every year. On this night God's decree for the whole year is brought down."
The Holy Prophet (s) answered Abudhar who asked about the Night of Destiny: "We will have this night till the Day of Resurrection"
Sunni interpreters also believe that the night of destiny will continue in this same manner.
For the third possibility it should be mentioned as a preface that in Islamic culture, the Night of Destiny is of paramount importance because of its unique features. There are many traditions in this regard mentioning that people should stay awake on this night and consider it as very important. One of these traditions is in the book "Iqbal Sharif" by Seyed bin Tawus in which the Prophet Mohammad (s) quoted Prophet Musa (a) who said: "O God I want proximity to you” God said: My proximity is for those who keep awake on the Night of Destiny." Moses said: "O God I want your forgiveness" God said: "My forgiveness is for those who forgive the poor on the Night of Destiny" Musa said:" O God I want deliverance from the fire." God said: "This is for the one who asks God's forgiveness on the Night of Destiny." Musa said: "God I want your consent." God said "My consent is for the one who prays two ra'kats on the Night of Destiny"
Sending down the Holy Quran, the angels and the spirit on God's apostles, is considered more valuable than one thousand months and specifying the destiny of God’s creation are some features of this night.
The question is whether these features are repeated for all people living in cities with time zone differences?
What can be interpreted from the Holy Quran and traditions is that the Night of Destiny is just one night and all of these angels were sent down to Imam (a) and specified the destiny for various things and the things which happened to the apostles of God and the infallible Imams on this special night only.
God says: “Therein descend the angels and the Ruh by Allah’s permission with all decrees” . The angels and spirit are descended on this night as is the Holy Quran: "Truly, We sent it down on the Night of Destiny."
We have this in traditions that God's decree for the whole year is sent down.
They say fulfillment of duties can open doors towards the perception of the blessings of this night. . Through reasons and various facts when the first day of the Month of Ramadan is specified, then the date of the Night of Destiny can also be determined. Certainly doing acts of worship and keeping awake on this night will bring down God's blessings even though that night is not the real night of destiny. It is recommended to keep awake on the last ten days of the month. The reason behind this Islamic tradition is for us to become aware of the importance of this night. The only question which remains is if the day of destiny is as important as the night of destiny? In response we should say that although some events like sending down the angels on the apostles of God (a) takes place on the night of destiny, the day of destiny is as important as the night of destiny.
The late Sheikh Abbass Qomi said in his rituals on the 23rd night: We should value the days of these nights too by praying and reading the Quran because we have this in reliable traditions that the day of destiny is as valuable as the Night of Destiny.
 Putting these two verses together “Truly, We have sent it (Holy Quran) on Al Qadr” and “Ramadan when the Quran has been sent”, we can interpret this.
 Surah Qadr Verse 1
 It is said that God has concealed several things among other things: The Night of Destiny among other nights, the Day of Resurrection among other days, the Supreme Name among other names, the time when the prayers are accepted by God among other times, God’s consent in all affairs, God’s saints among other servants, this is for the people to respect all nights, refrain from making sin at all times, respect all the people and seek God’s consent in all affairs.
 It may be that it was for this reason that the Holy Prophet (s) and the Infallible Imams (a) kept awake praying on the last ten nights of Ramadan. It may be said that the Prophet and the Imams were aware of the Night of Destiny and keeping awake on these nights had another reason. Possibly it was for teaching other people to be careful all the time.
 Sofian bin Samt asked Imam Sadiq (a): “Which nights are likely to be the Night of Destiny? Imam replied: “The night of the 19th, 21st, and 23rd. Dehghani, Akbar, Nasim interpretation, p. 465, Qom, Haram publications, 83rd edition.
 Surah Qadr, Verse 4.
 Tafseere Nemoonah, Vol. 27, P. 185
 Qomi Mashadi, Mohammad, Interpretation of Kanzald Ghaegh, Vol. 14, P. 359, Ministry of Culture.
 Fakhr Razi, Interpretation of Kabir, Volume 32, P. 29, Dar al Ehya, Beirut.
 Imam Khomeini, The Rules of Prayer, P. 333, 4th edition, The institute for the Dissemination of Imam Khomieni’s articles and writings.
 Tabatabaie, Seyed Mohammad Hossein, Al Mizan, Vol. 20, P. 332, Society of Teachers.
 For further information refer to:The Legal Interpretations of the Quran. Ibn Arabi, Vol. 4, p. 1961, Dar al Ma’refat
 Surah Qadr, Verse 4
 Surah Qadr, Verse 1
 Interpretation of Kenzald Ghaegh, Vol. 14, p. 359
 There is another answer to the third possibility: For example in the Tafseere Nemoone Vol. 27, P..193, the night is defined as the shadow of one part of earth on the other part with the full period taking 24 hours. Therefore the night of destiny may be the full period defined for the night i.e. the full period of 24 hours when the earth goes dark. Thus it starts from one point and ends in another. Based on this idea there will not be multiplicity of the Night of Destiny due to different time zones.
 Some traditions quoted on toleration in traditional proofs suggest this concept.
Hesham bin Salem quoted from Abi Abdullah (a): “If some one hears that a certain action at a given time will bring God’s rewards, and later it is proved that it was not the case, God will grant His reward to him anyway.” Al Qawaed Seyed Mohammad Kazem Mostafavi, The Society of Teachers, P. 96
 “The Night of Destiny happens every year and the day is as valuable as the night.” Sheikh Toosi, Tahzib al Ahkam, quoted from Nasim e Rahmat interpretation, P. 472, What has been mentioned in Tahzib is not the personal interpretations of Sheikh Toosi, it is quoted from the infallible Imams (a).
 Mafatih Al Jinan, P. 389, Published by Loghman Publications.