I live in Phoenix and went once in early August and once in mid October didn't find any living specimens. I found 2 dead females on the October trip there are alot of Xyloryctes thestalus, and I think another similar looking hornless species very hard to tell apart mistake them for female xyloryctes thestalus. I found 3 Chrysina Gloriosa on the August trip.
I think September maybe the best month for Dynastes Granti. Highest concentration of beetles is the Home Depot and that is where I found the 2 dead females. I didn't see any other collectors. There also seems to be a rush of beetles just at dusk and just after sun down and then alot seem to disappear but slowly you might see some different species trickle in like Chrysina gloriosa. Maybe try camping and setting up a light trap that is what I might do this year.