Naively, the average wait time from the perspective of the restaurant’s owner is 1 hour 2⁄7 of the time, so 2⁄7 of an hour, just over 17 minutes. Not bad, right?
However, if by average wait time I mean the amount of time waited, averaged over customers, then for every 5 customers that arrive Sunday through Thursday, 20 arrive on Friday and Saturday. So really 20⁄25 = 80% of customers are hitting busy hours, and the average wait time is 80% of an hour, 48 minutes. Not so good.
The standard term for this observation is “Inspection Paradox”, see e.g. this blog post.
The standard term for this observation is “Inspection Paradox”, see e.g. this blog post.