I have found that some batches will have a lot of drop out right off the bat, while others seem to go forever before any losses start to happen. I think it depends perhaps on the condition of the parents at the time of the particular birth.
I wasn't in any hurry to split them up for the first four to six weeks, depending on the batch.
I would start now hatching out the brine shrimp, especially if you plan to do the recommended decapping treatment.
If you bleach a touch too long they won't hatch out. Best to experiment until you KNOW you have it down pat.
You can filter off the live nauplii that you don't need now, and freeze them in on waxed paper so someday you can break off a portion, thaw, and add to the nursery with the live ones. Hopefully this will get them on to eating frozen foods sooner.