I agree 100%—the traffic in the late afternoon around Philly can turn murderous (it’s always bad) and with the need to return a rental car, you’re cutting it way too fine. I just looked at Google Flights and there is a convoluted way to go from Harrisburg to Tucson via CLT and DFW, leaving 4:58 PM and arriving 11:52 PM. Two connections at that time of day is also a risk, but once you’re headed west at least you will have more re-routing options.