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?