I did 12 in the past week. On site, it was about 20-25 minutes. The longest one took 40 minutes because the store was so busy, I couldn't get a picture of the counter (or ask the clerk for the phone number and hours - which weren't posted) for awhile. I did everything else while I waited, but it was a super busy location. The online report took about 10 minutes, mostly because this particular site was slow to load the photos and I could only upload 3 out of the 12 at a time or it timed out on me. They are quick and easy though.
This really depends on which audit you are doing. There are two or three long ones that take 30-40 minutes. Also, sometimes the same client will have more than one type of audit. It can be a long one with lots of photos or a relatively simple one, done in 20 minutes. You don't find out the extent of the work until you sign up and read all the materials.
The visit itself not too bad. Uploading pictures sometimes has been frustrating. In 10 years in doing them, can’t think of any bad experience with the personnel I have met I have done hundreds across 5 states