Can you provide a little more information on your experience? Such as:
What type of facility are you shadowing at? Outpatient surgery, hospital, pain clinic, etc.
You don't have to give away your location but is this a rural area or city?
What type of cases did you shadow?
Is it ok to assume the AA left because there was not any more cases for the day?
Answering these will help us (AA-C's and AA-S's) give you more information. From my experience I have only heard of such hours at outpatient type clinics or smaller surgery facilities. I can not think that larger hospitals would be profitable if their employees/staff left on a regular basis at this time.