You'll be safe to allow 2 hours unless the weather is terrible. For Snowmass the most convenient parking is at the Two Creeks base area, which is at the bottom of the lift which takes you to Elk Camp. You can park 100 feet from the base lodge and lift. The parking fee was about $7 last time I was there, but may be around $10 now. There used to be free parking in a shuttle bus lot on the access road, but this may have changed with the new base development. Parking at the Highlands is also very convenient and gives you access to the shuttle buses to Aspen. Last season it was free if you had 3 or more people in the vehicle, otherwise $7.00. I don't recommend parking in Aspen unless you are staying in lodging facilities there. Much of the on-street parking is either metered or by permit only, and the city parking ramp is pretty far from the lift.