Changing theme depending on (server) time

Can anyone help?

I’m re-designing a small community site, & it’s my first WordPress site. I’ve designed two skins, one for day & one for night, & I’d like these to change depending on the server time.

I’ve had a look for a plugin that’d do this (thought it was a long-shot) with no luck. Presumably the default skin for the site is in the db somewhere, but MySQL is my weak point, could anyone tell me where in the db this is stored? The plan is to put in a couple of cron jobs, so at 6am it’ll change to day, & at 6pm it’ll change to night.

Any help appreciated…