Is the prayer of someone who prays every prayer ten minutes before the adhan of the next prayer valid? And does the time for a prayer expire upon hearing the adhan for the subsequent prayer, or some time before that, and what is that duration?

The prayers performed by their owner at the end of their prescribed time, or after their time has elapsed as a make-up (qada'), are considered valid and absolve one from the obligation if their conditions and pillars are met.

However, delaying a prayer until after its time has elapsed without a valid excuse (such as sleep or forgetfulness) is considered a major sin and necessitates repentance. Some jurists are of the opinion that such a prayer is not valid if it was intentionally delayed without excuse.

It is not recommended to delay a prayer until the very end of its time; rather, it is disliked to delay it until disliked times (awqat al-karahah). Delaying the Dhuhr and Maghrib prayers until the very end of their respective times before the entry of the next prayer's time is permissible, but it misses the reward of performing it early. It is not permissible to delay the Asr prayer until the time of yellowing (isfirar) without an excuse, according to many jurists, because it is a time of necessity (waqt darurah).

The time for a prayer ends with the entry of the time for the subsequent prayer. The time for Fajr ends with sunrise, not with the Dhuhr adhan. The decisive factor in knowing prayer times is based on the cosmic, Shar'i signs, not merely the adhan or calendars.