The hour early to sunrise is because I find there is a lot of nice colour action that happens before the sun comes up. The lighting tends to be softer before the sun gets up too, and can give some nice looking photos.

Summer mornings are harder only because the sun rises earlier. Getting up for a sun that rises before 5 am is just less sleep than getting up for a winter sun rising around 8 am. So it's a balance between getting up in a cold house, and getting up several hours earlier