Is the 'Isha prayer invalid if performed at a late time, based on a different Fajr time than that of the location?

The time for the Isha prayer begins from the disappearance of the red twilight until the preferred middle of the night. The period between the middle of the night and the appearance of dawn is a time of necessity. Therefore, there is no impediment to delaying the prayer until the middle of the night, but it is not permissible to delay it past the middle of the night except out of necessity. The Prophet, peace and blessings be upon him, once delayed the Isha prayer until the middle of the night and said: "The time for Isha is until the middle of the night." It is not permissible to rely entirely on the calendar for determining prayer times; it is merely for approximation, and further verification is required thereafter. It is recommended to consult trustworthy scholars in Islamic centers to determine prayer times.