Why is the 'Isha' call to prayer delayed in Ramadan, and is the Maghrib prayer considered valid if performed ten minutes before the 'Isha' call to prayer in winter, or before the delayed call to prayer in Ramadan?

Prayer times are determined by fixed indicators that vary with place and time. These are the religiously authoritative means for determining the beginning and end of prayer times, and any other calendars are merely tools to facilitate knowledge of these regulations.

It is permissible for there to be a time difference between the call to Maghrib prayer and the call to Isha prayer, but the call to prayer must not be delayed beyond the beginning of its time, as it was legislated to announce the entry of the time, and delaying it might lead to deceiving the general public.

The impermissibility of delaying the call to prayer beyond the beginning of its time does not apply to the iqamah (the call just before prayer). Rather, the Sunnah is for there to be sufficient time between them for preparation for prayer and for the congregation to gather.

If the call to Isha prayer is given at the very beginning of its time, then whoever prays Maghrib a little before the Isha call will have prayed it within its time. However, if the call to Isha prayer is delayed beyond the beginning of its time, then it is not permissible to delay the Maghrib prayer until then.