You can apply after you've finished all your pre-reqs which is about two years. However, the field is getting highly competitive and with a bachelors, pharm schools consider you a more competitive candidate. Don't get me wrong, you can still try to apply after you finished pre-reqs, but many people who do that are asked to finish getting their bachelors before applying. I'm a first year, and considered taking that route of applying after two years, but i'll most likely get my B.S. before I apply.
Good luck!