I would put them in the tank they will be housed in. If there is no filter or air/water movement, it is not good for them. Bettas can withstand it as they surface to breathe air when needed. If you dont see any signs of illness I would say it is okay to add them. It is a good idea to observe new fish however. I dont have a qt for my FW
yet either. I should get one as my tank is larger and has many inhabitants. I try to observe fish in store as well... I probably look crazy staring into one tank for 5 minutes but it has worked so far.