Conditions for the validity of Salaah

Q: In our country, fajar prayer starts at 3.50am and magrib starts 6.50pm. What is the correct time to perform tahajjud prayer?

Q: A person goes to visit someone else and they read salaah in their house. Later on they discover that the qibla they faced in salaah was incorrect and was in the opposite direction. Do they have to repeat all the salaah they performed at the house (including in the past)?

Q: Can one read his maghrib and esha salaah in the time of maghrib before boarding the aeroplane considering that it is quite difficult for one to read his esha salaah on the aeroplane especially when there is no salaah facility on the plane?

Q: If I read tahajjud at 3 am, can I read any other nafil salaat. eg. Salaatut tasbeeh, haajat, etc. between tahajjud until fajr sets in.

Q: Is it permissible to pray salat wearing a t-shirt which contain a picture of human which is kept coverd?

Q: What is time of zawal and when does it start and end?

Q: If someone performs his salaah facing the wrong direction, away from the qiblah, does he have to repeat his salaah?

Q: I completed my Fajr Salaah at 6:16 AM. The time listed for sunrise on the perpetual timetable is 6:17 AM. Was my Fajr Salaah valid?

Q: Is it permissible to combine 2 prayers? Meaning, is it permissible to pray zuhr and asr during the time for zuhr? or pray zuhr and asr during the time for asr?

Q: Can we make niyyat/intention for chaast/ishraaq/hajat/shukur/taubaa when performing salaatul tasbeeh?