Be careful when going away from their suggestions. They have their reasons.
When leaving from the ladies trip, I went with their suggestion (going to LAX). I almost missed the shuttle, not because I was late, but because they had my name spelled in some way that I don't comprehend (I made the reservation online, and my name is ridiculous simple; you can spell it ALL sorts of wrong and it's still going to be SAID the same way) so she didn't think I was going on her shuttle, AND I guess I was a touch too close to a pile of luggage with a carseat, so she didn't realize I was alone (and her fare was one person). I practically had to force my way on her shuttle, and thankfully I had my confirmation page printed so she could look up my number and see that I was the person on her shuttle.
After that, I spent *at least* an hour on that shuttle, going back and forth, up and down Harbor. Picked up pre-booked person after pre-booked person, and we were early to each place, so we had to wait for each group of people.
Now it was pleasant...most of the people on the shuttle had been to a natural products seminar and I had scads to talk about with the friendly people, but it could easily have been an hour of misery.
By the time we finally got to the airport, I did NOT have the 2 hours or 1.5 hours I wanted there before my flight. If I had set my own schedule based on what I felt it would take, time-wise, I would have been absolutely late for my flight through no one's fault of my own.
So be CAREFUL when messing with their times. They have their own schedules, and they put in plenty of fudge time, just in case they have their shuttle as packed as they did with me. I know that it's a special brand of torment to be way too early for a flight (one time I was very early and then my flight was delayed by hours!), but ultimately it's better to be too early than too late.