Asalamualaikum. 

Hazrat, as you know my wife is not able to fast because we recently had a new baby.

Alhamdulillah, she tried her best to get Tahajud in, but there are times when she misses it because of the timetable I follow, where the sehri end time is 1:30am. The reason for this is because she is making my sehri breakfast if you want. In such a situation, is it permissible, if she can follow another Hanafi timetable where the start time for Fajar is about an a hour, or so ahead (2:45am) approx, so she can get Tahajud in.

Or, is it the same principle with fast, where one can only follow one timetable for sehri, and Fajar?