Dp works 7am to 4pm from home.
He never ever needs an alarm clock to wake up. He regularly falls asleep at 8pm on the sofa and is awake at 4 or 5am after going up to bed at 10.30pm ish with me.
He then used to toss and turn and wake me up (I don't need to get up til 7am). Since I was so sleep deprived, I had to ask him to not wake me up when he wakes up, he now gets up and watches TV downstairs or in the other bedroom for 2 or 3 hours or so in the morning. If he wakes at 4 or 5am, he will then insist on having a sleep at lunchtime or at 4pm and believes in doing so he is doing me a favour by not falling asleep in the evening and actually having some quality time with me - I don't normally sit down til 8pm after housework, dinner, homework etc.
Over the Christmas period (when he gets 3 weeks off), he can go to sleep at the same time as me and will wake at the same time as me but he just can't seem to lie in to any sensible time any other time of the year. Even if we go away for the weekend, he will be awake at 5am watching TV and then want to come back from a day out to sleep in the afternoon!
I just think if he knocked the daytime naps on the head, he would probably sleep better at night.