We love love love Buffalo airport. We are about 30 minutes from the border so we leave with a 3 hour window. Our upcoming trip has a 5:15 pm flight, so we'll leave here at 2pm. That gives us a nice cushion for border traffic since it's a Friday evening, or if we are stopped. It's only happened once for a non-Disney trip but it delayed us an hour to go into customs so I like to have extra time.
Best case scenario, we sail right over and we're at the airport in under an hour. That gives us 2 hours to check our luggage and go through the security line and grab something to eat. Like the pp said, there will likely only be one or two places open if it's very early. Usually there is one right at the beginning of the long hallway that sells coffee and bagels etc and one down near the end. We love the one down at the end which is called "Which Wich" and it opens at 5a.m.
We grab a drink for the flight and something to eat and then usually sit on our laptops or tablets and charge them. There's plugs in the walls where you wait, right up against the windows. We make sure we have a full charge for the flight and eat our breakfast. Generally they start boarding right around when we finish eating.
It is a wonderful airport for ease of use and we've used it at least 20 times in the last 6 or 7 years. Peak times can be very congested to go through security. Our Christmas week flights had massive lines and sometimes first thing in the morning the security line can be long because they are just reopening for the day and can be moving the 5, 6, 7am flights through.
Normally though we are through security in about 10-15 minutes.
So I may be overly cautious with my time estimate but I would far prefer to sit and wait comfortably than be rushing in and find a line at the border or in security.