nicer DV cameras don't auto turn off, you can use software to capture a frame every X time. the cheaper cameras do auto turnoff.... UNLESS (hehehe) you put a tape in with the record tab set to save, then they never shut off, they keep putting out a warning the tab is set to save. :D
I thought some of the not too expensive Canon point and shoots came with an intervalometer function.
In the end though the camera and the timer is not the only problem. You need a housing to keep the elements out, power and somewhere to mount the unit. There was a complete system for sale on eBay, built by someone in New Zealand if I recall correctly. All built into a Pelican case with a window. Asking price around $500. For the work put into the unit quite reasonable really.