For knowing the time to stop eating and drinking, I rely on the adhaan of the mosque that is near us, but I notice that there is a difference of five minutes between it and the timing of the electronic adhaan that I have on my cell phone, which is based on a well-known program called al-Baahith al-Islami. My question is: if I rely on the adhaan of the local mosque, which is later than the electronic adhaan on my cell phone, will my fast to valid, or should I rely on the adhaan on my cell phone and stop eating and drinking before that?

Praise be to Allah

If the mu’adhdhin gives the adhaan at the usual time of the adhaan in your
city, which is based on the common timetables, and he does not give it
later than the time given in the timetable, whether that is due to a
mistake on his part because he is not precise, or it is based on his own
ijtihaad and opinion – rather his adhaan is in accordance with the
timetable that is used in your city – then there is nothing wrong with
your relying on his adhaan, even if it is later than the time given in the
timetable of the program mentioned. 

But if the mu’adhdhin is not known to be careful and precise in following
the timetable, then in this case you cannot rely on him, and you can rely on
the timetable of the program mentioned. 

However, to be on the safe side in all cases, you should pay attention to
the timetable of the programme, because it is known that this program is
precise and trustworthy. 

That is because making the mistake of being too early and refraining from
eating and drinking a few minutes before the adhaan is less serious than the
mistake of eating and drinking when dawn has broken, based on the other
timetable. 

Shaykh Ibn Baaz (may Allah have mercy on him) said: 

If
he hears the adhaan and knows that the adhaan is usually given at the time
of dawn, then he must stop eating and drinking. If the mu’adhdhin gives the
ahdaan before dawn breaks, then he does not have to stop eating and
drinking; it is permissible for him to eat and drink until it becomes clear
to him that dawn has broken. 

If
he does not know whether the mu’adhdhin gives the adhaan before or after
dawn breaks, then to be on the safe side it is better for him to stop eating
and drinking when he hears the adhaan, and it will not matter if he eats or
drinks something at the time of the adhaan, because he does not know whether
dawn has broken. 

It
is well-known that those who live in cities where there are electric lights
cannot know whether dawn has broken from looking, but to be on the safe side
they should follow the adhaan and timetables which state the time of dawn in
hours and minutes, acting in accordance with the words of the Prophet
(blessings and peace of Allah be upon him): “Leave that which makes you
doubt for that which does not make you doubt” and “Whoever guards against
the doubtful matters will protect his religious commitment from shortcomings
and will protect his honour from slander.” 

End quote from Majmoo‘ Fataawa Ibn Baaz (15/286) 

For more information, please see also the answer to question no.
66202 and 66891 

And Allah knows best.