All depends on where you want to be in the rope drop crowd. I seldom, if ever, head to a bus stop between 45 to 10 mins before park opening. The buses are jammed with others. If you want to be in the front of the rope drop crowd, you need to be at the bus stop no later than 45 mins before park opening. An hour is best. That way, you'll be among the first to get through the turnstiles.
I like to get the bus at a few mins before park opening..that way the crowds for the bus and the crowds at park opening have gone. But...I seldom need to be there for rope drop anymore.