The first bit of time you need to think about is when their pickups are. We took it last Saturday, and our plane landed at 9:40, when the bus left terminal 1 at 9:30. The next bus was at 10:30. To make sure we were among the first on, we slowly got our stuff and walked up to Terminal 1, where it starts pickups.
At last it got there, then we had to deal with it stopping at each terminal (there are something like 7). So don't bother getting excited until you're done with the terminal stops.
From there they estimate an hour to get to the area, but that all depends on traffic.
What they do once in the area seems to differ widely. In our last experience, they got to the DLH first, the people who take tickets/money got on, then we all stayed on board and they started dropoffs at other hotels. In our case, GCH was first, then he said he'd be going on to the Sheraton next b/c it had a tricky dropoff area. Other people have had very different experiences.
Don't get me wrong, I actually quite like the bus...the drivers, while a bit "off" in personality, have been much safer-feeling than SuperShuttle drivers...but it's not a FAST thing. And in fact, even though we like LAX, we've decided that when we go again, we'll save up the extra money (even when base rate is the same, it seems the taxes and fees pop up the fare by at least $20 each passenger each way) to get into SNA, because it's so much closer.
We landed at 9:40 and checked in to the hotel at around noon.