<< I have heard of people starting their rides at, like, 4:00am and ending them at 11:00am to avoid the scorching heat. Is this common practice? >>
As a resident of the hottest part of AZ, yes it's possible to ride summers that way. What you might be forgetting is that you won't be able to pull in from your ride and camp in 100+ degree daytime heat. It doesn't cool off that much when the sun goes down either (that's why early morning is best for riding), can stay at 100+ til midnite. Plan on motels. Pre-check routes & distances carefully before you go. Call ahead & make sure that the motels / restaurants you're counting on will be open. Lots of these businesses in AZ are seasonal - open winters when hundreds of thousands of snowbirds (retirees from cold climates) are here, closed summers. Motels that remain open will most likely be verry slow & happy for the business and let you check in early.