GPS time signal information is received automatically whenever all of the conditions described below are satisfied:
- The current time is between 6:00 A.M. and 10:00 P.M.
- The face of the watch has been exposed for about one or two minutes to continous light equivalent to the brightness near a window on clear day.
- All time calibration signal receive operations performed during the previous night were unsuccessful.
After exiting the Airplane Mode, position information will be acquired automatically from GPS when the conditions below are satisfied
- The time is between 6:00 A.M. and 10:00 P.M.
- The face of the watch is exposed for about one or two minutes to continous light equivalent to the brightness near a window on a clear day
This information can be found on page E-33 of the manual. If the watch isn't synchronizing with GPS time automatically, then its possible that at least one of these conditions wasn't fulfilled. For example, the user might have been wearing the watch indoors. This means that the watch isn't being exposed to sufficient enough sunlight to act as if it was outdoors (and therefore in the line of sight of GPS satelites). In that case, you can trigger a manual synchronization to ensure that the GPS sync is working properly.
You can also find more details at the following Link: