I would be really upset if Rowdy had to sit in the groomers all day - when I had an appointment. I think if you have to make an appointment for a specific time, then they should groom the dog in a reasonable amount of time from the appointed time, like 1-2 hours, max.
I love my groomer, but I can't make an hour appt., just a day appointment, and then it is first come, first serve - so I just get Rowdy there first and he is done in an hour or less. She calls my husband who goes to pick him up. Now, if I can't get him there first, then I know that he will have to stay for several hours - and that has only happened once. And it is my option to not drop him off and wait till another day when I know I can get him there first.
I don't think you are unreasonable at all. I would have been really MAD!