Shadowing Follow-Up

I know there are a lot of threads about how to find shadowing experiences but I couldn't really find one that answered my question. Basically, I emailed a couple of PT clinics yesterday asking if I can shadow someone there and my question for you guys is how long do you think I should wait until I follow-up with a call (Assuming they don't reply any time soon)? Also, how can I avoid sounding pushy when I call asking for an update?

Thanks in advance for any help