I too am amazed by all the early birds. When w*rking, I struggled to get to the office by 9 am. Just a natural night owl all my life.
When I Fired, I started getting up around 10 am or even noon, largely because I went to bed at 2-3am. Since moving to AZ, I surprised to find that i now go to bed at 10-11pm and awake around 6-7:30 am.
I think that the sunlight is so bright down here that it wakes me up early (normal for the rest of you), and I naturally tire by 10 pm since I've been up so long. Besides, when the daytime high is 110F, I'm eager to get outside as early as possible while temperatures are comfortable, or at least tolerable. I thought about installing room-darkening shades, but decided that I love getting up early to enjoy the wonderful mornings in SE Arizona. I've become a morning person, and my morning coffee on the patio is the highlight of my day!