according to the provider.  I would suggest you start your initial contact three to four weeks in advance to at least get screened... caveat while in the travel mode is always... always... always... have a plan b, plan c... but foremost with doing this is to be honest with the ladies, tell them you are visiting their fair town and are thinking of scheduling with them while there.  Just as you would hate a no call, no show situation so would the providers... after several years in this hobby, I have well established ladies in the cities I travel to, so this issue has gone to the back burner for me.

I say never too early if they do book that far ahead.  January isn't that far.  If you are sure of who you want to see, I say go for it.  The worst they can say is contact them later.

What ever you can do to show the provider that you are serious will assist you in getting her to be serious about making sure she is there for you.

Don't be a nudge, but a reminder a couple of weeks in advance, another a week before and finally the day before will make sure that they don't NS you.

Not 100% guaranteed, but then again what is?

i took a trip to Vegas recently for three nights, contacted three different providers through e-mail about a week before my arrival date, and was able to set up a date for each night of my stay - all in the same day!  one of them even phoned me that day to say hi and that she hoped i wouldn't be disappointed when i met her.  and boy, i was NOT.  incredible lady.

this is not to say that scheduling will always be this easy, or that a week in advance will always suffice, but it worked for me, at least this time.  i did have some backup choices to pick from in case a date didn't work out, which most hobbyists would agree is something you should always plan for.  be prepared!

hope you have fun.  the ladies i saw in Vegas were absolutely superb.  i plan to return soon!