It really depends on the pharmacy, but I think to expect an employer to train you for only 3-4 hours of weekly work isn't realistic. It'll take you months to pick up all the essentials of your job if you're only there 3-4 hours a week.
My suggestion is to try to time a tech job so that you can work more hours per week during training. Try to start it over the summer, for instance. That way, if you want to keep working 10-15 hours per week while you're in school (which, I think, is a realistic number of hours to be working for a pre-pharm student) they may be more accommodating. Bear in mind, if you're asking for a small number of weekly hours, they may anticipate that you'll be more flexible as to when you can work those hours (evenings, weekends, etc.) So don't go in to an employer and say, for instance, "I can only work from 9-12 on Thursdays, can I have a job"?
If you can't make that work with your schedule, you may want to consider volunteering; in that case, a pharmacy would likely be just fine with 3-4 hours per week.
