What is the extent of the beginning of the prayer time? Is it half an hour?

Performing the prayer at the beginning of its time yields great reward. There is no established legal limit for advancing it by half an hour or otherwise. Rather, some scholars have interpreted it as performing the prayer after confirming the entry of its time and after offering the regular supererogatory prayers that precede it, such as the four rak'ahs before Dhuhr prayer, and this is done after preparing for it.