Try Yellow Dog. They have a program in many locations where they'll pick you up at your hotel and take you to fish locally.
Yellow Dog Fly Fishing Adventures - Mexico: information - Bozeman, MT
Getting to Ascension Bay will take you a couple of hours from PM; possibly longer. Boca Pailla would be the closest outfitter on the strip down from Tulum.
We fished out of Pesca Maya a couple of years ago and loved it; both the fishing and the lodge/people.
You might want to think about stretching your time to a full day; even if you have business commitments. You can do a lot of business at night over dinner; when the fishing is not as apt to be a competing concern......................