Times of Salaah

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?

End of Zuhr time

Q: What time does Zohar Salaah become Qadha. Does Zohar end at the time Asr starts? I see that the Shafi time for Asr is 15:15 and for Hanafi it is 16:03. I do understand the the shadow of an object needs to be twice the original size plus the bit that was there at midday. I am asking in regards to the times for the Salaah. This is the time in Durban.