Performing the obligatory prayers before their prescribed time begins is not valid and is not permissible. Prayers must be performed within the times determined by Allah. Performing a prayer before its time does not fulfill the obligation; therefore, such a prayer is invalid.
However, if a prayer is missed, it should be made up later (qada).
In situations where it is not possible to perform prayers on time, one may, due to necessity, combine the prayers (jam‘).