Is it Islamically permissible to offer the Isha prayer an hour earlier in the summer – so that it is performed at 10:30 instead of 11:30 – in Europe where its original time is delayed?

The times for the obligatory prayers are determined by cosmic signs, and they are as follows: Fajr (Dawn) Prayer: From the appearance of the true dawn until sunrise. Dhuhr (Noon) Prayer: From the sun's zenith (when the shadow begins to incline eastward) until the shadow of an object becomes equal to its length. Asr (Afternoon) Prayer: From when the shadow exceeds the length of the object, according to the majority of scholars. Maghrib (Sunset) Prayer: From sunset until the disappearance of the red twilight, which is the most preponderant opinion. Isha (Night) Prayer: From the disappearance of the red twilight until midnight, and until Fajr prayer time if there is a necessity.

It is not permissible to perform the prayer before its time, nor is it permissible to delay it, except for a valid legal excuse.