CO_Pilot's instructions will be the easiest. However, if you have your heart set on the colectivo, they park across the street from the Commercial Mexicana store, which is on Tulum. Basically take the R-1 bus out of the hotel zone and it will eventually turn down Tulum. When you see Commercial Mexicana on your right, get off. The colectivos will be lined up in the parking area across the street from the store. They go to Playa but will stop in Puerto Morelos. It's about 25-30 minutes. The colectivos stop outside of town about 2 miles, so from there you take a cab into town (20-30 pesos). You'll want to tell the driver you're getting off in Puerto Morelos, as they charge a little bit less than if you were going all the way to Playa del Carmen.

Thank you for the info. I missed seeing your replies earlier. I was hoping that the colectivo would be quicker/easier than taking the R-1 and then getting the ADO, but that doesn't sound like that's the case. Thank you again!