I confirmed for the move at 4:00pm, and the seller and I both got home early. When I called at 4:15 because they hadn't arrived, the owner referred me to the driver's cell phone, who in turn said that they had a 2-hour window to arrive and that they'd be there by 5:30 (which turned out to be 6). That was annoying, though luckily neither we nor the seller had evening plans. I can understand a time window given inexact delivery schedules, but this was not communicated to us prior.
Once the piano movers arrived, they were very professional, courteous, and helpful. They offered to take a bit off the price for the misunderstanding although we paid in full for their good service rendered.