I've seen a variety of opening scenarios: opening the ticket readers (right at opening time); opening the ticket readers a little earlier and letting people bunch at a rope drop (at the top of the hill were you make the left to go to future world); and I've even seen opening the ticket readers (about five minutes early) and letting the International Gateway people get a head start to meet the main entrance people on a more even keel.
And no, you can't walk around the lake (roped off).
But you can enter early if you have a tour (and your name is on the list).