I was astonished when, arranging a tryst with a gentleman that I've known for a *very* long time, I realized that he had assumed that I would not be available to him on weekends. Weirdly, it had just never come up before. I told him that of course I was just as much available on weekends as any other day, and he pretty much echoed the OP's assumption that most ladies aren't.
I had never heard that before.
It makes sense on some level. If a woman has kids home from school, a husband who is home from work, or civie friends who plan their events on weekends, then those days probably get a little crowded. As for me? My dog does not go to work or school, and most of my friends are equally as active any day of the week. It never occurred to me that I *wouldn't* see someone on a weekend, especially because hotel rates in the Boston burbs are so much lower on weekends.
I'm also an extreme night owl, meaning that I'm much more likely to be awake at 2am than 8am. Combined with the fact that I absolutely hate traffic, meeting at 10pm is perfectly fine with me - the only shortcoming being that most good restaurants are for some reason closed by then.
Of course, it's not like I'm sitting in a hotel room somewhere with an "Open Late" banner hanging from the window like a Wendy's drive thru! Regardless of the time or day requested, I generally have at least a few days of anticipation for every date.