i always u-lock mine to the rack. This keeps it from being stolen, and i can relax and enjoy the ride. However, i ride my route from start-to-end, so i have plenty of time on each end to get the bike on/off. But i can load and lock pretty quickly, so it's not a big issue at a middle of the line bus stop, which i sometimes do. Just have the lock in your hand and unlocked, ready to go as the bus approaches. Same goes for any gear you are taking off the bike, have it off and packed away so that you are not fumbling with things.

I've never had a driver give me any lip about how long it takes. Just be quick.