In the desert, you often really don't want to be walking midday, but if the moon is out doing 20 miles in a night isn't too bad, and doing it split over two days is fine. 5 or 6 liters of water plus some food would be plenty, depending on what you have available to carry that ~15 pounds splitting into two days may be more comfortable. Either way, infinitely less risky than building a motorcycle.

4 mph takes talent, especially over distance. Andthat’s on hard surfaces. From what I understand walking on sand is deceptively taxing. I’d say 2-2.5 and not as the bird flies distances. So ten to fifteen hours of walking if your feet let you.