The current time is not a function of your Edge 800.
It recieves the time from the satellite.
You can only set the time zone or 24/12hr format.
Page 14 of the manual
GPS units are passive - meaning they only recieve information - they do not transmit. The time is kept on the satellite, and cannot be adjusted manually.
You'll likely notice you are exactly HOURS ahead or behind your actual time.
This is because the ZONE is improperly set... or the DST is off.
Check those to be sure they are correct.
If you're not sure how this is done - a Master Reset will straighten out the unit and then you can go through the inital setup to properly set your time zone and DST setting.
There are a few instances in which you may want to perform a master reset on your Edge 800, such as:
- not receiving a satellite signal
- want to restore the factory default settings
- not functioning properly
All settings, workouts, and satellite data may be erased when resetting the GPS. Workouts can be backed up to such training programs like Garmin Connect or Training Center. Refer to the FAQ article "How can I backup my personal settings and profiles on my Edge 800?" to back up your personalized settings.
To perform the master reset:
- Power the device off
- Press and hold your finger on the upper left side of the display
- Power the device on while still maintaining pressure on the display
- Release on the display when the Reset device settings to factory defaults? message appears
- Touch Yes
The Edge 800 is now reset. You will want to leave the device outside with a clear view of the sky for a minimum of 20 minutes to acquire satellite data.