Well it depends on the time used. Now if they had to search around on the car (without a diagnostic computer) then its usually labor per hour used. Now if it was a simple (from a code reader), then 1 hour worth of labor.
In the shop I worked for, we had to tell the customer that they could be charged for up to an hour of tech time and if was going to go over that, we would call, let the customer know what the tech had found so far, and if needed, request authorization for additional time. The techs diagnostic rate was 108. an hour. Just depends on what kind of issue was diagnosed and if it was resolved. Electrical issues seemed to take the most time.