I don't use brine shrimp but I think you should keep the air on and I personaly think you'd get better results if you fed them right away - what are they for? If they are for fry, I'd suggest microworms for future use. They are much easier (not to mention cheaper) to raise/harvest and you don't need to buy eggs each time. There are also fewer risks involved with using them and they last much longer in the tank. If it's for fry, they are also generaly easier for the fry to catch and eat.