As Robo said, there are too many variables to answer for certain. But if you're there an hour before and you know what you're doing, there is a very good chance you'll be on and off the ride in under 30 minutes.
We arrived at 6 for a 7am opening. We hit a snafu of bag check not opening until nearly 6:40, meaning a couple hundred people without bags got in before us, despite arriving much later. If you go without bags, this won't be an issue. Then, since we were not at the front of the pack, we couldn't all get at the front or near the front of the line at various turnstiles, meaning we had to wait for each other to scan and get in before we could start walking towards the tree of life. The bigger group you are with, the more difficult it will be to walk fast and prevent others from passing you. Despite all of this, and a sitting on the ride about 5 minutes while they fixed someone's seating in another room, we were off the ride by 7:20 and walked onto NRJ.
Of course a latter opening means more people willing to get there early.