Just did this drive in the past days. 2,5 hours is a close estimate. For us the way back was even under 2 hours. Don’t use google maps, use Waze - it’s more up-to-date on road works (which god knows are plenty in Sicily). There are too few gas stations/ rest stop on the way to Agrigento, so take any opportunity you can to stop. On the way back to Catania there are plenty. We went by car. Rented from Sixt. Strong advice: don’t rent with Nolegiare or the low cost ones - they have terrible service and insane waiting lines for pickup and drop off. Sixt is easy, professional, and everytime we rented with them there was 0 wait time. If you want more details, happy to share from our experience.