You are right it is an appointment system, and again correct -- the size of the vessel determines how much the fee as well, so does how quickly you want to get through. Also other determining factors- for insgtance they group smaller vessels with larger ones, so that a small vessel does not just transit the canal by itself-- that would be very wasteful. It is a bit like Dr appt in that you set up the time and date ou will be there, however this Dr can choose to make you wait while others who paid more go ahead of you.
Long story short- we will be waiting for a good week to get through it would seem- how else do you explain the fact that the vessel is due in Ensenada in 2 weeks time and yet the distance involved is closer to a 5 day trip?