Times of Salaah

Q: What is the latest one can start his Salaah in order that the salaah be considered as adaa'? If one starts his Salaah in the Salaah time, and during the salaah, the time ends, does the salaah get invalidated or does it count as qadha?

Q: My question relates to the times of Tahajud. When i was in madressah I was taught that we could read from just after 12am till about 15min before fajar salah. Recently I was told many different things regarding the times. What would be the right time to read Tahajud salah and the cut off time?

Q: What is the time of Zuhr Salaah?