What focal length are you intending to shoot at? I've done a few timelapses at 10mm and after 30s or so the trailing starts to become apparent, but is fine really...in fact a small star trail isn't that noticeable in a timelapse...it almost enhances the effect of motion.
As Chris says, a few seconds will get a few stars. I shot The Pleiades the other day at well under a second and was getting a few of the stars to appear, but this was at 600mm. 20 or 30 seconds at sub 20mm focal lengths and the aperture as wide open as possible will get plenty of stars in the frame...hundreds or thousands even, and also you'll get some Milky Way definition.
Be interested to know how you're going to put the images into a timelapse video. I've used Photoshop Elements before, which is pretty good, but wondering if there's anything better which is widely available.
Good luck, and let us see what you manage to create.