Use the middle of the day to scout and also find the little details. It's also a peaceful time to simply vegetate, listen to the silence (if you are away from the crowds), enjoy the peacefulness.
If there's still a bloom you may find some color with which to work. You'll most likely find the flowers on the upper alluvials if you are lucky. With good craft using flash, reflectors and gobos, you can shoot them any time of day.
Travel into the canyons, such as Titus and Natural Bridge. There you may find opportunity for details and coolness during the mid day. That said, the flat light of the day can be pretty sublime and to do it justice takes good vision.
In any case, don't simply let the light slide. There a lot of Death Valley and not enough daylight to see it all at the shoulders of the day!