UPDATE 2: Firmware released by Panasonic has now fixed this problem. You can download the update at http://panasonic.net/avc/lumix/pressrelease/gh3_lens_firmware/
UPDATE: (March 1, 2013): Panasonic has confirmed the intervalometer bug and will soon be issuing a firmware fix, which should make the GH3 a fantastic camera for timelapse!
We are discussing this issue in the forums. From the original article (February 13, 2013):
The GH3 is a wonderful camera. And it has great potential for use as a timelapse camera once a few issues get sorted out. For a lot of timelapse, people will use an external intervalometer or motion control rig to control the shutter release on the GH3. But when shooting a static shot, or shooting a hyperlapse, the intervalometer built into the GH3 is the best solution. Or at least it would be… if it worked correctly. It doesn’t.