Its Groundhog day....again...
I saw this thread, and decided it was time for my annual viewing of Groundhog Day.
One of the interesting things about the film is that it is never actually said exactly how long he was there. In one of the initial ideas in the screenplay, Phil kept track of time by reading one page of a book from the library every day, and he made it all the way through every volume, so that would imply thousands of years.