Well you're in that camp too - build in extra time!
Actually, it all depends on the route, of which I'm not familiar with for this half. I know for the Princess (which used World Drive to get to/from MK) I had a heck of a time getting to MK... was trying to be at the front gate at 7:45. I built in time and even that wasn't enough.
If you can, study up on the route (if it's out yet) and see if you think it'll impact you. You could easily have no issues at all, but could be subject to detours. Good luck!