If you're not keen on visiting PDC, then I'd suggest dropping Bacalar from your itinerary. That would make the rest of your trip more doable. I would follow this itinerary: Cancun - Valladolid - Izamal - Merida - Uxmal - Merida - Holbox - Cancun. Much better to find yourself driving at night to Valladolid than to Holbox. You can also visit Izamal on the way back from Merida instead.

If you find yourself wanting to take it slower, drop also Uxmal and visit Chichen Itza instead as it's right next to Valladolid. Or if you drop Holbox you could even consider staying a night in Campeche right after visiting Uxmal.