With one of my regulars (been meeting her for over a decade now), I've never had any problems. Its only because of a rare situation with this one though; She no longer advertises anywhere. She also has a full time (professional) career outside of her part-time escorting, so I can only book her on certain days (typically weekends). Not exactly same day appointments, but even if 1 day in advance of those chosen days I still never had any problems booking her. And I strongly suspect she only meets a handful of guys she has met in the past (all well established, long term regulars of hers. Never new punters).
With others who still advertise, can sometimes be a hit and miss. There again I hardly ever book on the same day anyway. As above, it tends to be at least 1 or 2 days in advance.