Is it possible to do time synchronization?

Question

Java

It is necessary to make time synchronization of 30 devices (so that the countdown on these devices starts synchronously, and now there is a big difference in the beginning of the countdown).
How can this be implemented directly in the program? (i.e. set the same time on all devices)

Answer 1

How can this be implemented directly in the program? (i.e. set the same time on all devices)

You will not be able to perfectly synchronize the timelines. Because synchronization is a network operation, and desynchronization will include network propagation time (which fluctuates randomly).
Naturally, synchronization with NTP on the WAN will be much rougher than synchronization on the LAN.
Once upon a time, I did synchronization of hosts in the LAN, and by means of a certain (simple) mathematical processing, it was possible to synchronize the time scales with an accuracy of microseconds (up to 10). But this was done in the QNX real-time OS, in Linux it will be worse, but not by much. And your Android is Linux.

Answer 2

you need to google in the direction of "delay / latency compensation algorithm"