When is the last time to perform the Dhuhr prayer if its entrance time is 12:30?

The preferred time for Dhuhr extends from the sun's zenith until the shadow of everything becomes equal to its height. This is considered an optional time. Whoever prays Dhuhr during this time has prayed it within its prescribed time, by the consensus of scholars. If you are unable to discern the signs, ask someone who knows the beginning and end of the time, or rely on the beginning of the Asr time, as whatever precedes it is considered part of the Dhuhr time.