You need a sustainable temp of about 145-F.
Sanitary on blacktop? Use a piece of aluminum foil.
How long will it take? Well, one factor is the initial temp of the egg, the temp of the surface, the reflectivity of the surface, the ambient temp, the amount of cloud cover, how thick the piece of foil is, etc. ...
This "experiment" has been conducted many times ... usually with failing results. If it was going to work ... you would have a better chance in Phoenix than in just about anywhere else in the US.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain