When does the last third of the night begin and end, and is it permissible to pray ten minutes before Fajr?

The last third of the night is determined by knowing its beginning (sunset) and its end (Fajr dawn). Then, the total time is divided into three parts, and the third part is the last third. Obligatory prayers should not be performed before their prescribed time, as the entry of the time is a condition for their validity. Therefore, the Fajr prayer is not valid if performed before its time. As for the night vigil (Qiyam al-Layl), it is permissible until Fajr dawn.