5-20 minutes to actually look over the game. Another hour or so to chat with the seller if they're feeling chatty. 30 min to an hour to break it down and get it out, depending upon how easy/hard it is to move out.
When selling, I usually allot 2-3 hours for a potential late arrival, looking over the game, chatting, and loading up.
People who own pinball machines just seem to be very friendly most of the time.
I've also been a part of rush pick-ups where the game was all ready to go, so the stop was only 15-20 minutes.
I usually buy project machines, so that assessment is usually different than buying a working game for top dollar. I look over the artwork, wear, circuit boards, backglass, and check to see what's missing (if anything). I'm not usually concerned about how well it plays since it's a dead game most of the time anyway.