How can I tell when they're done?
When they hatch, you will be able to see them moving around.
OK thanks. Next question... how do I feed them without raising the salinity in the fry tank?
Net them from the tank/container they are in, rinse them in tap water, toss them into the tank in which you are feeding.
Wouldn't they fall through the net?
You will probably need to purchase a brine shrimp net. They are made of a finer material than fish catching nets. Or, use a handkerchief placed inside a regular fish catching net.
Ahh. Wonder if cheesecloth would work...
Yes it would.