Conditions for the validity of Salaah

Hanafi performing asr salaah in Shaafi'ee time

Q: When we go for umrah, all the umrah busses stop for asr prayer according to shafiee time. We (ladies) strictly follow hanafi time. In winters, due to school, we read our zuhur salah after the shafiee asr azan, as hanafi zuhur salaah time is still there. We also read our asr according to hanafi time i.e. late.

So my question is... the bus stops for asr at shafiee time. If we do not get the jamaat, what should we do? Can we read at shafiee time at such circumstances? 

Next salaah time entering while one is performing salaah

Q: I am currently excused (chronic excuse) with regards to wudu due to bleeding. I know that my wudu breaks when the next prayer time comes in. However once or twice I took too long to pray and when I checked the time, I was a few minutes into the next prayer time. Are those prayers invalid? Would they be invalid if I wasn't excused with regards to wudu?