If you keep BBS in the water they hatched in they won't last very long (12 hours maybe), filtered into dechlorinated fw they will live for 5 or 6 hours.
You can freeze them as soon as possible after they hatch and then use them whenever you like (use ice cube trays).
You can also grow them out in a seperate tank/container using water of the same salinity as the hatch water and an airstone, feeding them with artemia food. But it can be difficult to judge how much food to give - they basically need both food rich water and clean water at the same time. As the Brine shrimp grow they molt and this causes the water quality to drop quickly so you need to keep doing water changes.
If you're using the BBS for newly hatched fry then the best is to use them as soon as possible after they hatch as that is when they are the most beneficial to the fry due to a yolk sac that they have (they use this up in the first 12 hours).
I start a new batch of bbs at least every 2 days, I harvest the first batch after about 18 hours, filter them over the hatching container and start the air again as soon as I've finished filtering. The filter paper (coffee filter) gets washed in dechlorinated fw which I then let settle for 5 minutes after which time the bbs are mostly at the bottom of the container, I then suck them up into a syringe (the kind you get for giving medicine to kids) and then feed them to the fry - 10 fry get 5 drops of this 'concentrated bbs'. If you time it right you can use the same hatch 2 or 3 times through the day (the third feeding will more than likely be dead but the fry don't seem to mind). Any left over each day go into my community tank where all the inhabitants seem to enjoy them as a 'snack' (bit like popcorn!).
Then repeat the next day and start a fresh batch off ready for the 3rd day and so on.
I'm not sure how big JD fry are when newly hatched (I have Endlers livebearers which are probably a bit bigger) but they will most likely take the fresh bbs without a problem, feed 2 or 3 times a day (start with just a couple of drops of the concentrated bbs), shouldn't take long to figure how much they can eat at each feeding, you'll see the fry go from skinny to fat in a matter of minutes untill they look like little blobs floating around. As the fry grow you can increase the amount you feed each time.
Hopefully you've got the fry in a bare bottom tank cos you'll need to be able to siphon out the uneaten food at least every couple of days or the water quality will suffer.