We're planning an overnight stay in Cedar City to break up the journey from Moab back to Las Vegas for our flight home the following day.
I've checked Google Maps and know travelling time given probably isn't accurate. It's at least a 4 hour drive to Las Vegas.
I'm a bit risk adverse and I'd want to be much closer than a 4 hour drive for a morning flight. But, it is what it is for you.
I think you should leave Cedar City by 6. AM to give yourself a bit of a cushion on the other end.
If it's a 4 hour drive you should leave at 7am, you gain an hour. I drive that regularly and it usually takes 3 hours elapsed so 2 hours on the clock to drive at the speed limit, it's miles on the freeway and even with the lower limits in the gorge and traffic in Vegas you can easily average 60mph.
Our flight home is early afternoon 2pm. We will leave Cedar City early as advised, as we always like to build in an extra cushion of time. If journey time is 4 hours, taking into account time zone loss of hour, we should arrive 9.