Dear Hesham,

May I ask for what reason do you need the satellites to be synchronized in time? What application is requiring this? Earth observation? Then, go for GNSS-based time synchronization, as done by EO satellites in LEO: https://navi.ion.org/content/69/3/navi.531

"GNSS signals could even be used for reliable navigation in lunar orbit", so also for time synchronization: https://www.nasa.gov/missions/tech-demonstration/nasa-navigation-tech-shows-timing-really-is-everything

It seems that as long as your device can have a GNSS receiver, that's the best way to keep it time-synchronized. Is there anything preventing the use of GNSS on your intended application?

Regards,

David