I haven't used an alarm clock in five years. I live on a 24 hour clock and cross time zones all week.
I drive a truck with my husband. He usually drives days and I drive nights.
I get the best sleep I've ever had in my life. Usually a solid 7-10 hours a day.
My body just wakes up when it is ready. Generally I wake up around 7 in the evening. I usually drive from around 8 pm to 6 am.
Then I work on my writing (or I read) until I get sleepy.