Oh yeah, I've used the interval timer on the K-5 quite a bit (called an intervalometer), and it's a huge amount of fun. Here's a 5 hour sequence, one picture every minute, 20 sec exposure, which is 300 pictures. Combined into a 24 frame per second video clip:
http://www.bsquires.name/ph/test4.mov
This was taken in the Deschutes River canyon, just south of the Columbia River in Oregon, USA The light pollution is the I-84 freeway I think, but it's at least 5-6 miles away and not visible to the naked eye. K-5, 15mm Ltd, f/4.5, 20 sec, every minute for 5 hours. Turned everything off, auto white balance, auto ISO, image review, beep, shake reduction, etc, etc. Cannot turn off the red "writing to SD card" light though...
The flash at the end is a train going through the canyon at about 2:30 am.
My one real complaint with the K-5 is that you cannot save a User setting on the mode dial, and then use the intervalometer. Seems really dumb. It's a pain to switch everything, and I mean everything, to manual or off, when doing shots like this, and then back to normal operation when done with the time lapse.