Definitely weekdays. Work helps camouflage extracurricular activities...

Most of my opportunities are during the week, especially those where I can plan ahead a day or two. Weekend opportunities are less frequent and tend to come up without much notice, making it hard to book in advance.

but Bravo for the subtle Ad ...

Weekends are always better for me. Work consumes me and I prefer to be freshly showered before an appointment.

As my work schedule is unpredictable through the week. Also, so that I'm well rested, and not burdened with any stresses from the day. And...since I have to travel an hour plus each way for appointments....it becomes a huge block of time to have to free up...much more easily done on the weekends.
I have the luxury of not needing to find reasons to disappear...lol!

for locals I think is better during the week, before 6pm (that way you can take ur own personal time on a lunch break, a late afternoon meeting or to evade the traffic jam.  
Outcalls are usually Monday-thrsuday in the evening, after work dinners, conferences, etc. (if no plans, I make dinner dates pretty fun).  
Weekends are rare, usually early sat morning in certain areas (Tysons, Arlington), before some go to play golf... or after their sports activities.  

Some holiday weekends will be busier than others. But that goes for non-holiday weekends too.
8-5/9-5/9-6 on a M-F have always been a bit more popular but there's no major shortage of folks to step out on the weekends.  
My availability locally for the most part is after 5 on weekdays (due to my civvie career) unless a longer appt "motivates" me to take leave if you will and my weekends are often way more open so...pretty much anyone who wants to book me is pretty much already familiar with my schedule.  

... is usually hard for me to find.  I usually play on Friday evenings.  It’s too difficult during the week with variable work schedules and deadlines.  My weekends are either working on the house, studying, or catching up on work.  That leaves the occasional Friday evening, normally breaking up the drive home from a meeting 75 miles from home.