For a multiple hour appointment it could be a few hours to a few days. With the last minute half hour appointments 1/2 hour advance. If I am traveling it will be weeks in advance.

two or three days with an indie if she is touring or again just one day if she's local. I try not to schedule too far in advance and it's pretty rare that I get told that she's booked solid.

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My primary ATF visits DC every two weeks, and I always, always, have her first appointment.  So effectively,, it is always two weeks notice with her (or however many days specifically, as it can vary by a few each visit).

Another ATF visits DC every 10-12 weeks and same deal, I always have her 1st appointment back here pre-booked, so effectively two months.

If I am trying out a new-to-me-provider, I am typically contacting her either the day before or more likely the day of because that is very likely to be an "impulse purchase" for me.

With a traveling gal I want to see, I'll schedule with her when I first find out she's coming to my area, whether it is someone I have seen before and she lets me know, or whether I see her advertising on the local board.

Similarly, if I am going to be traveling to a gal's city on business, I'll contact her as soon as I know I'll be there.  That is sometimes months in advance.

With local gals, I schedule 1-2 weeks beforehand.

and June has a few dates set up already too.  

That doesn't mean that an impromptu trip to NYC, Chicago or DC won't necessitate a last minute call, but that's not my preference.

When visiting a hobby rich city I might make an appt weeks before arrival. When home my professional responsibilities do not allow for that kind of certainty so often I can only make an appt a day or two in advance.  And on occasion I'll have something change in my schedule and I might even attempt a "day of" booking.

One thing I will never...never do is book something unless I am reasonably certain I can honor the appt.

Too many things can happen. I don't REQUIRE it, I just tell the guy that I can't guarantee a meeting that far off, and that he should wait til the week of to contact me.

Thru December this year. The sooner I know, the better.  

If you are interested in a lady, the best thing to do is ask her how far in advance she accepts appointment requests. I'm sure she will guide you. That will give you a good idea for future bookings with her.

great thread with all the answers thank you

Some April and May dates booked

Works better for me if I plan ahead.