Pugwash: I took my Stage 1 on the 10th November 2008 and would have been starting this Monday at the college if I wasn't tied to my contract at work until June. Expect 6 months or so - I went through the application process relatively quickly (2 months in total from Stage 1 to Stage 3) as I had other job offers on the table and had to make a decision by a certain point.
Mike172: Since I don't have a PPL I can't say exactly, but it might help in Stage 3 and the learning of the motivation paper stuff, but probably not much else until you get to the college!