Conditions for the validity of 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?

Q: Our madrasah teacher once told us that we should wait for a while after Azan and pray around 10-15 mins later (i.e. she was trying to say one shouldn't immediately start praying after Azan). Is it true?

Also, my father told me that there's a Hadith that says that one should quickly pray after Azan. Is there such a Hadith?

Q: Is it permissible to pray asr salaah during the last 20 minutes between asr and maghrib? (If I didn’t deliberately delay it).

Q: Sometimes, when I am in a hurry, I make a wrong intention before I start my salaah. For example, when I am supposed to offer Asr, in a hurry I make the intention of zuhr and start my prayer. I then realise this mistake during my prayer. What should I do?

Q:

1. If sunset is 6.40, at what time should Salah be performed?

2. If sunrise is 6.25, what is the end time of Fjar Salah?

3. If magrib Salah is performed a few minutes early, will it be valid?

4. If in the absence of a watch, how do we look at the sky to know fajr and maghrib salaah times?

Q: If a person prayed without using their Qibla compass, but estimated the Qibla location, but found out they prayed in the opposite direction, is their salat valid?

Q:

1. If the asr time starts at 3.57 and sun sets is at 5.32, what is the mustahab time to perform asr and when does the makrooh time start?

2. If fajr starts at 5.25 and magrib starts at 5.34 what is the mustahab time to pray esha?

3. My salah app shows that sehri or tahajjud time ends at 5.16 and fajr starts at 5.25, Can I pray tahajjud between this time? 

Q: If one has oral surgery due to having a wisdom tooth removed, and therefore has constant bleeding in their mouth for days, are they allowed to join prayers? If so how long are they allowed to join prayers? Is it until the pain ends or until the bleeding stops?