We had an 8.30 reservation at a popular restaurant and arrived quite early (8.10--no traffic!), told the host we were there and went to the bar. At 8.30, I checked with her and was told the table was just signing its check. At 8.45, I cruised the tables and the table closest to finishing had just begun its dessert course.
She had just made up a story to fob me off.
I wonder, why do restaurants tell you the impossible just because it's easier than apologizing for keeping you waiting? For that matter, how much of a delay should be tolerated for a firm reservation time?