It´s a silly question for skiers visiting crowded resorts. The only chance is the first chair or, even better, the time before.
I have "my" lifts operated by a company I used to work with (friends remaining!) which run earlier than the official time. A quad has the chairs parked overnight and it takes an hour to arrange and check them properly. It´s 7-8 a.m. Then there´s a surface lift with 8-8:30 "lifties and friends only"-operation. The first people can ride up at 8:30 so that at least till 9 it´s safe. That way I have at 10, which is the really bad hour on the worst days, 3 hours of skiing. When training, 7:30-10 are the hours as well, at 10 the poles must be away.
Springtime or even summer is the same. There´s no question when: as early as possible. If I had a lift of my own I would be skiing from 5.
The only time I can ski later is when I´m privately on a glacier at the beginning of December. It´s the off-season there, few people, it´s cold and the sun low. It´s almost no difference between 9 a.m. and 3 p.m. If I happen to be there I enjoy the luxury of skiing noon-4 p.m. They are the only late-start days I can have. The rest is like working shifts in a non-stop factory.
Do I like it? Getting up as early as at 5 is what I normally hate and fortunately don´t have to do. With the prospects of the perfect slope with no people around I really don´t mind.