Does the fast of one who masturbates during the Adhan of Fajr become void, knowing that the Adhan might precede the entry of the time by a minute or more?

One must repent from masturbation. The fast is invalidated and a make-up day is required if masturbation occurs after the entry of the second dawn. However, if it was before that, the fast is valid. Janabah (state of ritual impurity) does not prevent the validity of the fast for someone upon whom dawn breaks while they are in that state, based on the saying of Aisha (may Allah be pleased with her): "The Messenger of Allah (peace and blessings be upon him) would wake up in a state of janabah from intercourse, not from a wet dream, during Ramadan, and then fast." If you doubt the entry of the time and masturbate, thinking that night remains, the fast is valid unless it becomes clear that dawn has entered.