Answer
(Fatwa: 1087/910/B=1433)
There is only one witr. Its time is from Isha to true dawn. If someone is sure that he would get up at the time of tahajjud then it is better for him to offer witr salah in last night after tahajjud. And the person who is not accustomed to get up in the last part of night he should offer witr salah after Isha. One should offer two rakah of sunnah muakkidah after Isha one should offer witr. The holy Prophet Muhammad (صلى الله عليه وسلم) used to offer witr salah in the last part of night after tahajjud. There is no difference between these two witr.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband