Cadillac 2005 XLR Owner's Manual page 242

Clock Adjust Menu
The following options are available from this menu:
HOUR/MIN.: Touch the up or down arrows to increase or
decrease the hour or minutes. If you touch and hold one
of the arrows, the numbers will advance quickly.
12H/24H: Touch 12H to set the clock in standard time
or 24H to set the clock in military time.
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GPS TIME: The current GPS time will be displayed to
the right of this screen button. Touch GPS TIME to
set the navigation system time to match current GPS
time. If the seconds for the present minute are greater
than thirty when GPS TIME is selected, the clock
will round up to the next minute.
Daylight Saving Time: Touch this screen button to
increase the time setting by one hour. Then touch GPS
TIME to save the new setting. If the screen button is light
blue, the daylight savings time feature is on. If the button
is dark blue, the daylight savings time feature is off.
TIME ZONE: The selected time zone will appear to the
right of this screen button. Touch this screen button
to toggle between time zones and select the desired
one. The time of the selected zone will be displayed to
the right of the GPS TIME screen button. To set the
clock to the new setting, touch GPS TIME.
If the system is not receiving GPS information, you can
still set the time manually as described above but
the GPS time and Daylight Saving Time features will not
be available.
Touch Return to go back to the previous menu.