Is doubt about the beginning of the time for prayer among the things that invalidate prayer? And thank you.

The entry of the prayer time is a condition for its validity. It is not sufficient unless one is certain that its time has entered or has a strong presumption of it. Therefore, if one doubts whether the time has entered, they should not pray until they are certain of its entry or have a strong presumption of it. If one prays while doubting the entry of the time, their prayer is not sufficient, even if it later becomes clear that the prayer occurred within its time, unless their presumption of the time's entry was strong; in that case, it is sufficient if it becomes clear that it occurred within its time.