Jenny the air stone being removed has nothing to do with making brine shrimp hatch. If you remove the air stone before they have hatched (other than for a short period of time) they would most likely not hatch. The eggs normally do not hatch in 24 hours at room temp, unless you keep your house abnormally warm.
If you want brine shrimp to hatch every 24 hours you need to add heat to the brine shrimp hatchery.
Two ways that have both worked for me:
Adding an aquarium heater to the brine shrimp hatchery or add a light with a 60 watt bulb over the top of the hatchery.
The light method works better if you put the hatchery inside another container to help hold in the heat. I use an empty 12 gallon aquarium (no lid on the aquarium). I can fit 3 of the 2 liter pop bottle brine shrimp hatcheries inside of it. I use a clip on type light fixture with metal shade and hang it so it is about 4 - 5" above the shrimp hatcheries.
I have had no problems hatching brine shrimp every 24 hours using those methods. If you can not produce brine shrimp in 36 - 38 hours or your hatches are very low, odds are your brine shrimp eggs are old or not high quality, or your salt/water solution is not the proper mix.
