Kyle you did not say what you were sticking the Ditra to. If it's ply then you must use rapid as the moisture would have been sucked out of the slow set adhesive before it had time to crystallize and set.
I always use Ardex AF200 (comes in a tub). It is a really really tacky glue. I also use a roller (like the pic above). The beauty of Af200 is that you can start tiling straight away.
If you tile straight away after laying Ditra with slow set or rapid and you have to lift a tile, then you run the risk of pulling the ditra up from the floor.