Well...I'll have to say--I agree w/the above poster.
We NEVER miss DTD. It is the highlight of any trip to Central FL, even if we are not doing the Parks. We absolutely love it.
It IS a little bit more expensive, but it's definitely about the atmosphere and just being "in" Disney. We love to stroll throught it--mostly the Marketplace side, not so much PI and the West Side.
My husband is a Ghiradhelli (sp?) fanatic, so we NEVER miss that one, and my kids have to get "spit" on by Stitch each trip.
It is, I'll agree, much better to hit it in the late afternoon and into the night. Much cooler, a little less crowded, and everything is lit up.
As for DQ, we went for the first time this past April. We got in line at opening, and we left at CLOSING! It was hard to believe we spent 12 hours in there, but we did!
You CAN come and go as much as you want, but be aware that if they reach capacity, which they did when we were there, you may not be able to get back in, and we, too, left w/plans to hit RFC.
However, what we found was that the food INSIDE was priced about the same as OUTSIDE (at the different restaurants). We walked all the way to RFC only to be told it was going to be an 1.5 hour wait. Then, we walked back to Fulton's and decided to eat there. Well, it was a long wait there too, and the experience turned out to be absolutely HORRIBLE (but that's another story in itself).
When we got back inside DQ, I checked the prices for burgers, which we at at Fulton's, and they were the same as Fulton's! We could have saved ourselves a lot of time had I known that!
So...ALL THAT SAID--depending on what time of year you go and what you want to eat, you may want to stay inside DQ. But, yes--give yourself an entire day alone for DQ, and at least 5-6 hours for DTD.
BUT DON'T MISS EITHER ONE! (Rumor has it DQ is closing in December and ESPN SportsZone is replacing it.)