ETA exactly 4 hours out

Navigator 15 running on Philips CED1800BT. GPS set to automatically update system time (and it does - altered radio time and then switched automatically adjust and time reset back to GPS time). In the Select panes screen Navigator 15 time is exactly 4 hours ahead of GPS. Looks like I'm in the incorrect time zone but there is not an option to set the time zone in Navigator 15