I think this is more dependent on the individual girl not the agency. Some are worse at time management than others despite agency efforts to wrangle them. Definitely not late night outcalls.... as long as they show up I'm happy.
The most punctual is YFL. YourFrenchLady. They went by many names. When I used them this was back in 2004 they went by Independent-Network and later Montreal Girlfriend. When you book a girl at 6PM the girl shows up at exactly 6PM. Not a minute less not a minute more.