It's not so much how long it will take you, but how you are being treated by the school. Are you getting continuity of instructor(s)? You should be aiming to fly with the same one all the way through your course with the odd exception. Are you booking lessons and having them cancelled? Are there other ppl students with the same problems? If you are getting messed about, consider other schools - it's no big deal to change schools at ppl stage and you should have a few options in your area.