Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 695)

Syncing Time Between Cameras
Preparing for Time Syncing
Syncing the Time
You can set the sender camera time on up to 10 receiver cameras. Note that even after
synchronization, a slight margin of error applies between sender and receiver camera time
(of ±0.05 seconds, at most).
Caution
Always use cameras of the same model to sync the time. Synchronizing the time
on receiver cameras is not possible with different models of the sender and
receiver cameras.
This feature will not be available after 2038.
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