All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The basic principle is that the time of prayers are known by the sighting of cosmic signs that Islam has made as a proof for the times.
In our view, the issue of calendars of prayer times is that the calendars adopted by trustworthy scholars are reliable and acted upon unless they appear to be contrary to the Islamic signs.
As for unknown calendars, which we do not know who did them and which have not been adopted by trustworthy scholars, then these may be used in knowing the time of prayer approximately but one should not rely on them completely. In this case, one should act according to what he is certain of or what he predominantly thinks about the beginning of the time of the prayer for whoever is not able to know the time with Islamic signs, because he does not know them or he lives in a city (or town) where it is not possible to verify the Islamic signs due to the abundance of lights. In which case, he should take precaution not to take the initiate to pray until he is certain or predominantly thinks that the time of the prayer has begun, such as sunset in Maghrib Prayer, for example.
Islamic centers have taken care of the issue of the calendar in the world as a solution to the problem of fasting and prayer. In this regard, you may refer to the calendar of the Islamic World Association, or Al-Azhar calendar, or the calendar of Karachi University and other trusted entities.
You can find on the site the Hijri calendar and prayer times in the country where you live.
For more benefit, please refer to Fatwa 163523.
Allah knows best.