What tweaks do you have installed that affect the clock (or anything related to time) or the springboard? You've got something going there that, when it starts (or ends), ends up conflicting with whatever else you have installed.
Have you tried turning off Mobile Substrate and seeing if the crash still occurs? That might help to see if it is indeed some tweak you've installed.
If you can't think of anything, could you give us a list of the tweaks you have installed? We might be able to see if anything could be the culprit.
Marilyn