The clock is large-status-bar-clock, it has a bug in its configuration if you tick "enable alarms" it will kill the desktop somtimes, otherwise it's stable. Don't do any changes yet, I've played with the theme before and know what do if it breaks. Any change to theme.xml that is not right can make the desktop in load/crash loop. I boot from SD so it's easy to take the card out, mount on PC and change back. It might be possible to use matchbox-remote to change the theme, sleep and change back, but I haven't tried it.