I am hoping to start my ATPL distance learning course very soon, and I am in a similar situation as that I could study full time as I only work part time. However from my research (correct me if I'm wrong) my understanding is that the learning organisation (ie the ground school) will only credit the student with a certain amount of study hours a week, (ie 15 or 20) and bearing in mind that you have to do over 600hours, ultimately the length of time it takes you will depend on how many hours you can be credited for a week. Ideally I'd like to get mine done in 6 months but I'm not sure that it is realistic. Anyway best of luck and I hope this helps a bit!