Time for Imsaak (Starting the Fast) when the Calendar Times are Different

It is permissible to eat, drink, etc. until one is certain of the time of Fajr (interpretation of the meaning): “…eat and drink until the time where the ‘white’ and ‘black’ thresholds of Al-Fajr is evident to you…” [Soorat-ul Baqarah]

So, this means it is permissible to continue eating and drinking unless it is evident for one that it is time for Fajr. Fajr can be defined as the ‘white’ light spreading across the horizon from the eastern side. If one was unable to sight Al-Fajr and there was no one else who could tell him about it through means such as raising the Azaan (The call to prayers), then one should follow the timetable that, according to the best of his knowledge, is the most accurate. This accuracy is usually established through experience or by asking experts or the earlier Muslim residents of the area.