Some providers will take same day appts if they have seen you before and have already screened you.  Many will not as they need time to sufficiently screen you.  Look at their website and see if you can determine if they will take a same day appt.

Swim

I had a gent whose schedule precludes his booking in advance.  He cannot hobby during the eves because of family obligations, but his work schedule will often result in unexpected down time (out of the office) and he uses that time to play.  He says it sure beats filling out paperwork between sales calls.

He called the first time and I was not available.  However, I told him he was welcome to try back at another time and he did.  We met on his third try.  He still calls last minute and sometimes I am available and other times I am not.  I know that a number of other ladies work this way also.  I am sure he has a few ladies that he sees and he goes down the list till one of us says yes.