I remove the egg plate 24 to 48 hrs after they are laid.Just make sure you use the water from the breeder tank in the hatching tank.You also need a used sponge filter in there,so the fry have something to feed on.
what I usually do when my fish are breeding is to wait until they have been taken off the
rock by the parents. and then syphen them out into a bucket.
like BUD SAID ^^^^^ use the water from the tank the fry/eggs are from otherwise they
will die. this way gets the best survival rating I think. good luck.