This actually shouldn't be a problem. It's not like you will be in Physics class from 9-5 every day, and many PT clinics do need aids to work into the evening and Saturdays. All of the aide positions I've seen are part-time and the clinics have a "pool" of aides that they use, based on their schedules. You may want to look into positions within a larger system of hospitals, if that's an option available to you; teaching hospitals are usually the most helpful. The clinic I did outpatients volunteering at, was part of a large system of clinics around the city. The aides were all undergrad students that would work at the various clinics during the hours that matched their class schedules. If I were you though, I would not put off your prereqs just to open a few more hours to work as an aide.