The earlier groups can sometimes be only one hour. I'm not sure if they're allowing 2 hours at any point in the day anymore since park hopping is not a thing.For sure. This is obviously a very rough estimate but if 40 boarding groups are given out in around 40 seconds, that's one second per group. Still, there was a party of 4 right behind me going in, although they probably call a few groups right away so those folks may not have been in group #1.
Still, the earlier the group the better for me since you only get an hour to return and at some point the heat will force me back to the resort pool. (I thought it was supposed to be 2 hours but I'm pretty sure it only gave me 1 hour when I was "called".)