Q: Right after I said the takbiratul Ihram for Fajr the timer for its end went off, but I continued and finished the prayer. Was it valid?
A: It’s best to offer the prayer just after its time begins however, it is caught with the takbiratul ihram made during its time even if moments before it ends. The prayer is not void if the time then runs out just after. Source: Sharh al-Muntaha