1st Chair (at whatever time) you've got a few diehard day ticket buyers and some of the locals/season passholders (the locals/season pass holders will usually be done with their day within 2 to 3 hours unless its a powder day when they may squeeze in an extra hour or so)
About 1 to 3 hours after 1st chair is when typically the masses of day ticket buyers show up for their usual 4 or 5 runs before lunch followed by another 3 or 4 runs after lunch. Most of them will be done with their day by 2/2:30
depends on the Mountain. If the weather is decent, there's typically a decent line at the Forerunner Quad at Stowe at 7:30 on the weekend and on a powder day, I've waited 20 minutes to get on the lift showing up at 7:30 because the line will start forming at 7:15.