I think this would have so much to do with what group makes up most of your clients, and the area you live in.
For instance, most of my clients are either retired, or visiting. This is an active tourist area.
Therefore, weekends are very busy: Fri, Sat, Sun.
Also, I don't have such a calling for evening appointments because my retired clients have no trouble coming in 9-5, M-F. I find this mix of clients gives me a fairly spread out schedule, with no one day getting too much attention, except during the heat of the summer, then Saturdays are by far my busiest. The spa where I work at, Wednesdays are the slowest. I tend to make Wednesdays my official day off.
For my few working folks, Friday afternoon/evening seems to be popular. Start the weekend off right!