Biggest problem with poor hatching are from using cysts that have NOT been properly stored. Stores tend to keep them on the shelves where they deteriorate fairly rapidly. Properly kept should be in a fridge, not on a shelf or hook.
I store the Brine Shrimp Direct cysts in my freezer, taking a small portion out to keep in the fridge for daily use.
I use a mix of sodium chloride (pure water softener salt) mixed 10 to 1 with epsom salts and dilute to 1.018. I use a light to get the cysts to break diapause and at around 80°F they pretty well start hatching at around 12 hours, more at 18 hrs, but some late hatching at around 24 hrs or a little more. You can harvest early and let the unhatched ones keep on until they hatch.