As much as I love DS, I don't know that I would ever want to watch the whole series in one sitting. In theory it might sound like fun. But I watched the whole series in one year back when I put together the slideshow that's now atop the Robservations board, and trust me, while I enjoyed it at the time, it was a gargantuan effort that I wouldn't soon want to repeat.
As for the running time of the eps, it's always been my understanding that they run 22.5 minutes. Though I've never actually checked out if that's true...