When to Pray Witr?
Question

When does the time of Witr end? Should I deliberately delay it until the time of Fajr?
Praise be to Allah.The time for Witr prayer lasts from after `Isha’ prayer until dawn begins. 
Once dawn begins, the time for Witr is over, based on the words of the Prophet (peace and blessings of Allah be upon him): “Pray Witr before morning comes.” (Narrated by Muslim, 754) 
Muslim also narrated from Ibn ‘Umar (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “Hasten to pray Witr before dawn.” 
Also, Muslim narrated (752) that the Messenger of Allah (peace and blessings of Allah be upon him) said: “Witr is one Rak`ah at the end of the night.” 
At-Tirmidhi narrated (469) from Ibn ‘Umar (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “When dawn comes, all the night prayers and Witr are over, so pray Witr before dawn comes.” (Classed as authentic by Al-Albaani in Sahih At-Tirmidhi) 
Al-Bukhari (472) and Muslim (749) narrated that the Prophet (peace and blessings of Allah be upon him) said: “The night prayers are two (Rak`ahs) by two, then when you think that morning (dawn) is about to begin, pray one (Rak`ah) and it will make what you have prayed Witr (odd-numbered).” 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said: 
“This indicates that the time for Witr ends when dawn comes, because it is a prayer with which the night prayers are concluded, so it cannot be done after the night has ended.” (Majmu` Fatawa Ibn `Uthaymin, 14/115)
Some of the scholars are of the view that the time for Witr lasts after dawn comes , until one has prayed Fajr, and they quoted as evidence the report narrated about some of the Companions, that they prayed Witr after dawn had come and before the iqamah was said for Fajr prayer. 
Ibn Rushd Al-Qurtubi (may Allah have mercy on him) said: 
“With regard to the time for Witr, the scholars unanimously agreed that the time for it is from after `Isha prayer until dawn begins, because that was narrated through numerous Isnads (chains of narration) from the Prophet (peace and blessings of Allah be upon him). One of the strongest such reports is that narrated by Muslim from Abu Nadrah Al-‘Awfi (may Allah have mercy on him), which says that Abu Sa`id (may Allah be pleased with him) told them that they asked the Prophet (peace and blessings of Allah be upon him) about Witr and he said: “Witr comes before dawn.” They differed as to whether it is permissible to pray it after dawn. Some of them said it is not allowed, and others said that it is allowed so long as one has not yet prayed Fajr. The first view was expressed by Abu Yusuf and Muhammad ibn Al-Hasan, two companions of Abu Hanifah, and Sufyan Ath-Thawri  (may Allah have mercy on them), and the second was expressed by Ash-Shaafa’i, Malik and Ahmad (may Allah have mercy on them). The reason for their difference of opinion was the actions of some of the Companions which differed from what is mentioned in the reports.  
My view concerning this matter is that what they did does not contradict the reports that have been narrated concerning that – I mean the reports which say that they allowed praying Witr after dawn . Rather they allowed it in cases where it needs to be made up, not as a regular practice. Their view would only contradict the reports if they said that this prayer could be offered after dawn on a regular basis. Think about it.” (Bidayat Al-Mujtahid, 1/147, 148)
Shaykh Ibn Baz (may Allah have mercy on him) said: 
“There are many Hadiths on this topic, which indicate that the time for Witr ends when dawn begins.” (Fatawa Ash-Shaykh Ibn Baz, 11/306)
For more about the Witr prayer, please see the following answers: 38230 , 14093 , and 216236 . 
And Allah knows best.