Conditions for the validity of Salaah

Q: I am taking an online aalimah course and because of time differences, South African time goes from before maghrib 6:00 to 8:30 after esha has already set in. The asaatizah have told us that we should leave for salaah and catch up with the missed portion of the lesson later.i.e. We definitely shouldn't miss our Salaah for classes. Our first lesson completes at 7:00 or 6:45 depending on subject and day. Can I wait for the first lesson to complete and then read my maghrib Salaah before the next subject or should I immediately leave the lesson and catch up later?

Q: I work in a non Muslim country and during lunch time; I go to my car and pray Zuhr prayer by sitting on driver seat without performing ablution (I do tayammum by touching my hands on the steering). Can my prayer be valid? I believe praying prayer like this is better than not praying at all.

Q: A family moves into an apartment, they use a well known Qibla finding app to locate the Qibla direction and pray. Months later a neighbour points out that the direction is wrong and they must face the other direction. The difference is about 90 degrees apart. What happens to those Salaah that were prayed in the incorrect direction, are they valid or do they need to be repeated? 

Q: Is it permissible to read namaaz with just a kurta and no pants and underwear underneath it?

Q: While performing Tahajjud Salaah, the time for Fajr enters. What should be done? Will these two rakaats suffice for the two rakaats sunnat of fajr?

Q: I need to know can we offer Zohr and asr, maghrib and esha prayer together? If yes than at what time?

Q: I traveled from Cape Town to KZN for work for approximately 10 days. My work requires much travel to far flung places like Durban, Harrismith, Van Reenen and Vryheid. Based on the locations of the work areas, can I combine my salaah for my entire stay in KZN or should I make salaah separately after three days?

Q: For how many minutes is the duration of Maghrib before Esha sets in. If, for some reason, the Maghrab salaah is delayed for about ten minutes, would it be valid or treated as Qazaa?

Q: I have a question, when you finish praying and in about two hours time you find some little  sperm (which is light like water). Do you have to repeat that prayer?

Q: A male has a valid reason for performing Salaah at home. For Fajr Salaah, should he perform it when it is still dark (like for woman at home) or when it is bright (like for men in the Masjid)?