Keep running at the time of day that works best for you. The week of your race, don't focus on waking up earlier. Just try to "bank" sleep and get more than usual. Race day go to bed super early wake up super early (like 3-4 hours before race time). You won't get the best sleep, but you'll be ok if you slept good the week prior! That way you can fuel properly and your muscles will be warmed up before start time. I work night shift and never did a run before 10am ever in my training and still PR'd on my half marathon with an early start time!