I was able to hack together the menu system this morning.

The two buttons are "set" and "select." Select advances through the menus and then back to the time display. Set changes the selection on any one menu item.

Hit select once and you'll be in the timezone setting menu. Here, you get to pick the base timezone offset, anywhere from -12 to +12 hours from GMT. The lettering is "th" which stands for "timezone hour".

Next is 12/24 hour time display.

Third is DST on or off.

Lastly is brightness. The display shows "brIGht" and set will cycle through the brightness settings.

When you plug the clock in, it displays "no SIG" - no signal - until the GPS receiver gets a lock ("no SIG" will return if reception is lost).

Of course, none of this matters if you define HACKADAY_1K. For that, all you get is a 24 hour GMT display.