I'm going to stick with 30-45 minutes before posted opening time at all of the theme parks.
That way, when they do open the gates early, you won't be standing behind quite as many other guests who arrived earlier than you.
It also greatly depends on the general crowd level on the dates that you go.
In the "off season," (whenever that is, anymore) you can have a bit less urgency to get there "early" than when the place is flat-out overrun.