Time of witr in Jam' taqdiim

If a person combines Ishaa and maghrib jam' taqdiim (which is permissible during traveling) where he prays the Ishaa prayer along with the maghrib prayer during the time of maghrib, then the time for witr begins after he completes the Ishaa prayer.

This is the view of the Shaafi'i school of thought. It is also the opinion of the Hanaabilah.

قالوا: ولو جمع المصلي بين المغرب والعشاء جمع تقديم، أي في وقت المغرب فيبدأ وقت الوتر من بعد تمام صلاة العشاء

Kuwaiti Encyclopedia of Fiqh

Volume 27 Page 292