If it were me, I would wait until it appeared that they were going to swarm (queen cells along the bottom of the frames (assuming you are using the frames which came with the hives), take out the queen and a frame of brood and somehow attach some frames with brood and bees to a top bar and shake a lot of the bees in the top bar hive. This might seem like a swarm to the bees in the Dadant and they will go on and make a queen. It will probably be a month before the new queens are out, mated and laying. Or you could make several nucs with the remainder of the Dadant with time for the nucs to gather enough surplus to make it through winter. The TBH with the queen will take off because you have a mated queen ready to start laying so it should build up quickly. At least, that is what I would do. If you are only putting top bars in the Dadant, then half your problem is done. If the bars are a bit too short for your top bar hive, some long screws heavy enough to stand the weight of a top bar in the ends of the top bars and just take the frames out of the Dadant and put them in the TBH and let them go to work. At least, I think that is what I would do.
Your first effort should be to make sure the new Dadant has enough stores to make it through the winter. Keep a check on it and if they make it through the winter, you will be ready for the swarming season and your top bar hive.
Your first effort should be to make sure the new Dadant has enough stores to make it through the winter. Keep a check on it and if they make it through the winter, you will be ready for the swarming season and your top bar hive.