Looks good. Have you tried stracing it or running it overnight on batteries to see what it does to your battery life?

Hopefully, looking at the screenshot it's sleeping for a minute before updating the display...

Edit: duh, it's got a seconds display, so it won't be sleeping long at all. You probably want to remove that, or at least make it not update the display, and sleep for much longer periods when the screen is blanked or the application isn't in the foreground. There are DBUS events for both of these.