I guess it depends on availability but occasionally I get some that turn up and want longer than originally requested.
Last week I had one that booked an hour, a day or so in advance.
When he turned up, his plans had changed so he only wanted 30 mins. I made it my mission to make him cum and get out asap.
What do you do in these situations? Just for me, it puts me about, as I have mentally prepared for that particular duration.