RBs are hit and miss even in advance. Last minute ones leave too much to chance.
Before travelling, I look up aw to see if there are any interesting profiles in the area. If it's a fairly big city, I just text when I'm free without prebooking and can usually find someone. Often, outcall costs are significantly higher so if I need to I'll take a cab for an incall.
If I'm interested in a particular profile, or there's limited choice, I'll contact them a few days in advance, suggest an approximate time and confirm on the day.