I've done the drive down to Oro Valley from my office near the airport in 1-1/2 hour. That said, it was mid-day on a weekday.

Will you be alone, or with another passenger? Having another passenger will be extremely helpful, as you'll be able to use the HOV/Express lane once you get into the Phoenix area.

With returning a car, I'd plan at least 2-1/2 hours, maybe even 3. You'd probably be early, but you never know. Once you get close to the Phoenix area, that stretch of I-10 (anywhere from Riggs Rd to Chandler Blvd) will be extremely busy, all the way through the Broadway Curve (just past the airport exit). There's an HOV lane that starts around Chandler Blvd, you could stay in it until around 40th St (the rental car facility is signed from the I-10), and it would save you some time.

I'd suggest listening to traffic once you hit the Eloy/Casa Grande area. If there is something MAJOR on I-10, you could (normally it would be longer) take the AZ-202 San Tan Fwy (just before Chandler Blvd) East to the AZ Loop 101 North (Price Freeway), to the AZ Loop 202 (Red Mountain Freeway) West. That is a longer route (and no to minimal HOV lanes), but keep it as an option for a worst-case scenario.