How can a Muslim residing in Pakistan determine the correct prayer times, especially when hearing the Dhuhr adhan from several mosques at different times?

Prayer is obligatory at specific times, and the time for Dhuhr begins when the sun passes its zenith and inclines towards the west. If it is difficult to ascertain the time by the legal signs, one can follow a trustworthy, just, and knowledgeable person concerning prayer times, or a reliable muezzin who calls the Adhan after the time has entered. The Adhan of another muezzin at a later time does not matter, as long as the Adhan is within the prescribed time.