Today's Muslim world league calendar shows dawn prayer (Imsak) at 5:34 and sunrise at 7:12, Egyptian General Authority of Survey calendar shows Imsak at 5.26 and sunrise at 7:12 for Istanbul. 1- What's latest time to stop eating to begin fasting?2- What is the earliest time for Salat ul-Fjr?

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.

Imsak, i.e., abstaining from anything that breaks the fast, begins from the rising of Fajr (dawn) as Allah Says (what means): {And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night].} [Quran 2:187]

And the time of breaking fast is when the sun sets, as Allah Says (what means): {Then complete the fast until the sunset.} [Quran 2:187]

As it is known, the time of Fajr and sunset varies from one place to another place and from one season to another season.
Basically, a person should rely on his own observation of Fajr and sunset. If one faces difficulty in doing so for any reason, then he should rely on a trustworthy Muath-thin (the person who calls the Athaan), otherwise he may follow a calendar issued from reliable Muslim authorities to know the times of prayers and fasting.

For more benefit on Imsak before Fajr, please refer to Fatwa 82474.

Allah knows best.