Climbing is easier in the cold - your hands / fingertips don't get as sweaty and adhere better to the rock face.

Also, the dawn wall is full in the sun for much of the day, and the rock can get insanely hot during the summer. They need to climb before dawn on warmer than average days, or they would make no progress whatsoever. .

Other comments have covered the advantages. Disadvantage is that they have to face occasionally falling ice.

I haven't seen them mention the size of fragments they're facing, but they aren't wearing helmets. Either not large enough to be dangerous, or a helmet would make a finicky climb difficult and distracting.

Friction is higher in the cold. Especially for granite which faces the sun. You'll find lots of the hard routes are done in cold temps.v this is especially true in bouldering where the routes are very short 10-30 feet but with extremely hard moves.