Laylat al-Qadr is more likely to be in the last seven days. Ibn ‘Umar (may Allaah be pleased with him) reported that a man among the companions of the Prophet (peace and blessings of Allaah be upon him) was shown Laytal al-Qadr in a dream, and that it was one of the last seven nights. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “It seems that your dreams agreed that it is one of the last seven nights, so whoever wants to seek it, let him seek it in the last seven nights.”
(narrated by al-Bukhaari, 1911; Muslim, 1165).
Muslim reported: “Seek it in the last ten nights, and if any of you are weak or unable to do that, then let him not miss the last seven.”
It is most likely to be on the night of the twenty-seventh. It was reported, in a hadeeth narrated by Ahmad from Ibn ‘Umar, and a hadeeth narrated by Abu Dawood from Mu’aawiyah, that the Prophet (peace and blessings of Allaah be upon him) said: “Laylat al-Qadr is the night of the twenty-seventh.”
(Musnad Ahmad and Sunan Abu Dawood, 1386). The view that it is the night of the twenty-seventh is the opinion of most of the Sahaabah and the majority of scholars, and Ubayy ibn Ka’b (may Allaah be pleased with him) used to assert, without saying “in shaa Allaah”, that it was the night of the twenty-seventh. Zurr ibn Hubaysh said: I said: What makes you say that, O Abu’l-Mundhir? He said: by the signs of which the Messengers of Allaah (peace and blessings of Allaah be upon him) told us: that the sun rises that morning with no visible rays. (Narrated by Muslim,2/268).
Many marfoo’ ahaadeeth were narrated which said that it was on this particular night.
Ibn ‘Abbaas (may Allaah be pleased with them both) also stated that it is the night of the twenty-seventh. He reached this conclusion by means of an amazing process. It was reported that ‘Umar (may Allaah be pleased with him) gathered the Sahaabah together and included Ibn ‘Abbaas even though he was very young. They said, “Ibn ‘Abbaas is like one of our children. Why have you brought him here with us?” ‘Umar said: “He is a youth who has a good mind and who asks lots of questions.” Then he asked the Sahaabah about Laylat al-Qadr, and they agreed that it was one of the last ten nights of Ramadaan. He asked Ibn ‘Abbaas about it, and he said: “I think I know when it is: it is the night of the twenty-seventh.” ‘Umar said, “What makes you think that?” He said, “Allaah made the heavens seven, and the earths seven, and the days seven, and He created man from seven, and He made Tawaaf seven (circuits), and al-Saa’ee seven, and the stoning of the Jamaar seven.” So Ibn’ Abbaas thought that it was the night of the twenty-seventh because of this analysis. This has been soundly reported from Ibn ‘Abbaas.
The fact that it is usually the night of the twenty-seventh – and Allaah knows best – does not mean that this is always the case.
It could be the night of the twenty-first, as mentioned in the hadeeth of Abu Sa’eed quoted above, or it could be the twenty-third, as mentioned in the report of ‘Abd-Allaah ibn Unays (may Allaah be pleased with him) quoted above. According to a hadeeth narrated by Ibn ‘Abbaas (may Allaah be pleased with them both), the Prophet (peace and blessings of Allaah be upon him) said: “Seek it in the last ten days of Ramadaan, when there are nine days left, and seven days left, and five days left.”
(Narrated by al-Bukhaari, 4/260).
Some of the scholars thought that it is more likely that Laylat al-Qadr moves and does not come on a specific night each year. Al-Nawawi (may Allaah have mercy on him) said: “This is the apparent meaning because of the conflict between the saheeh ahaadeeth on this matter, and there is no way to reconcile the ahaadeeth apart from saying that Laylat al-Qadr moves.”
Allaah has concealed this night so that His slaves will strive to seek it, and will strive hard in worship, just as He has concealed the hour of jumu’ah, and so on.
So the believer should strive hard during the days and nights of these ten days, seeking Laylat al-Qadr and following the example of our Prophet (peace and blessings of Allaah be upon him), and he should strive in making du’aa’ and seeking to draw close to Allaah
excerpts from http://www.islamqa.com/index.php?pg=...&article_id=49