These are my experiences, to date, with various transportation options, going to various resorts...
DME....average of 70 mins from plane to resort. Most times were around 60 mins, but one time it took almost 90 mins. That is with 5 or 6 trips on DME.
Towncar...carryon bags only, 45 mins.
Towncar...checked bags, 60 mins
Mears shuttle.....(last Sept, so the newer shuttle not of yesteryear!!), 80 mins.
As you can see, the towncars are faster, but when you add in baggage handling, it is close to the same timing. Here's the thing...if I'm paying for a ride to my resort (i.e. a towncar), I want my checked bags with me. I don't mind waiting those 4 hrs or so to get my bags delivered if I ride the DME bus because I'm not paying oop for it.
But, if I'm paying $100+, I want those bags. So, that will add about 15 mins to my time...hence the 60 mins vs 45.
So, let's say your flight arrives on time, at 6pm. If you use DME, and tag your bags, you should be at POP by about 7:15, at the latest. I've taken DME to POP 3 times now and only one time was POP not the first stop. So, plan on it taking you until 7:15-7:30 to get from your gate to POP...then, when you arrive at 7:10, you'll be thrilled.
You should be able to be at the bus stop, waiting for the DTD bus, by 8pm. Your bags may not get to your room until 9-9:30, but your room will be available so you can head there, freshen up, head out to DTD and your bags will be there waiting for you when you get back to the room later on.
If you use a towncar, your timing will be similar....you may be able to knock off 10 or 15 mins but not much more than that.