About half my calendar fills in 4-6 weeks in advance. My regulars usually book first, along with professional gentlemen who see me as a professional like any other. They book their doctors, dentist, and therapy appointments 4-6 weeks out and likewise they are able to commit to an appointment with me far in advance.
2-4 weeks out I receive another 25% of my bookings. These gentlemen may travel for work and do not know their schedule more than 2-4 weeks in advance or just needed a couple weeks to think about it and/or put aside play money in their budget before they book with me. Or they just didn't notice my ads any earlier. I start advertising visits about six weeks in advance but not everyone checks the boards every week.
I receive very few bookings 1-2 weeks out from a visit. Most of the guys who like to pre-book have already booked. Maybe one booking will roll in during this time frame in any given city. Maybe a cancellation also. It tends to even out.
Within the week leading up to my visit I generally receive several more bookings from guys who do not know their schedules until the week before or so.
I'm theoretically open to last-minute bookings when a gentleman contacts me in exactly the way I desire and the stars align for both of our schedules. But to be honest, last-minute bookings are not my priority. I practically live on the road and I enjoy having balance in my life, which means that between my other appointments, I am shopping, eating out, or visiting civvie friends who I have in any given town. Since I travel so much, I have civvie friends all over. So I'm not inclined to interrupt my personal life to accommodate someone who couldn't be bothered to reserve time in advance. But as mentioned I will happily take last minute bookings if it all just works out perfectly. For example, sometimes a gentleman emails me from his work account with at least 3-4 hours notice and I happen to have an opening later that day that I can fit him into. But I turn away 80-90% of my last-minute requests.
How far in advance is too far in advance? If someone tries to schedule something with me 3-4 months in advance, I generally do not know my schedule yet. But if I'm advertising a visit, that means I am accepting appointments.