Depends on which schools you are applying to. Many have rolling admission, so applying early gives you a large advantage. One school I applied to pretty much told me I would have gotten an interview had I applied earlier. So check to see if your school does this. If it doesn't, then just get it in anytime before the deadline.
Your application will not be reviewed until you have your letters of rec in. So I would try to start getting those around the time you start filling out your application so that the letter writers have time to submit. Sometimes they are quick about it, sometimes they are not.
Other than that you can start applying at anytime once the cycle starts, so you might as well start early. Nobody will see it until you submit. Plus you usually have to submit a secondary/supplemental application directly to each school in addition to the PharmCAS app. And don't forget that some very good schools don't use PharmCAS and you have to apply to them directly.
