i know I will be in a city and want to set up my first hobby experience.  How soon before my "date" should I notify the provider before?  One week?  Two weeks?  Three? or should I make it for a couple of days before?

Thanks for any help you can give me.

The sooner the better, you want to give the provider plenty of time to fit you in the schedule. If you want too long there is a chance the provider you are trying to book will not have time for you

For a well reviewed provider you will need to contact sometimes two to three weeks in advance.  Why, she may be going on a tour or be booked solid.

sometimes the schedule changes at the last minute and I have to scramble to see someone.  Luckily most of my travel is to the same cities over and over so I am able develop a list of ladies for each city.

I would start with an e-mail contact a week or 2 ahead.  
In my last such contact, I marked the contact "advance screening".  I briefly stated that I was for real, the approximate date & time I had in mind for the proposed meeting & provided some information.  After a couple of e-mails...  we were set except for the 24 hours set up.  (The lady does not set dates over e-mail.  I gave her the number I would be calling from, so she could connect our contacts with the call.)  I called & the date was on, she gave me directions to the second call location.
 
I called, she directed me & the date went excellant.  (I'll be seeing her again.)
skb  

I usually contact the provider I want to see at least a  month in advance. If you wait until very close to when you will be in the city, she may be booked already.