Recently, I bought a bus ticket for Greyhound, which gives me 20 minutes at the Buffalo bus terminal (see Why is a change of carrier on Greyhound no transfer? ).
I am a bit worried now, will this 20 minutes be enough to make the transfer? What is the worst case scenario?
I don't know about Buffalo specifically, but with the exception of a few gigantic cities, bus stations are usually not large places. Often they are just one big room with a dozen or so places outside for buses to park. I can't imagine it will take you more than a few minutes to find your next bus and board.
So the only risk is that your incoming bus might be late. Unfortunately, I don't know of any way to estimate that risk - it would depend on where you are coming from, traffic, and how conservatively Greyhound has set the schedule. I am not sure that they publish on-time statistics for their routes.
If your inbound bus is late and you miss the connection, Greyhound should put you on the next bus headed for your destination. That's the worst case scenario. You'll have to check the schedule to see how long a wait that might be - it could be as little as an hour or so, or as long as a day or two.
