Is it permissible to pray Fajr immediately after the adhan?

A Muslim may pray immediately after hearing the adhan for Fajr if the muezzin is just and knowledgeable of the prayer times. However, it is advisable to wait several minutes after the adhan as a precautionary measure, because current prayer timetables may be ahead of the actual time due to the abundance of lights that prevent the sighting of the true dawn.