When does the time of esha end?

The time of esha ends at subah saadiq (i.e. when the time of fajr commences).

In some calendars the last time of sehri is explained to be 5 minutes before the fajr time enters. This is done as a precaution so that people do not exceed the time limit of sehri. The time mentioned in the calendars is an estimation. It is possible that they could be a mistake in their estimation and calculation. Therefore, as a precaution, the Ulama advise that one stops eating a few minutes (e.g. 2-3 minutes) before the time of subah saadiq mentioned in the calendar and one opens the fast a few minutes (e.g. 2-3 minutes) after the time of sunset which is mentioned in the calendar.

And Allah Ta'ala (الله تعالى) knows best.