Today is one week since I poured water over sand to see if anything would grow. My Triops have hatched, grown rapidly, and now range in size from 1/4" to 1/2". The largest is one that I transferred into a separate fish tank. I'm guessing it grows faster due to the higher oxygen content since there is a bubbler in the fish tank and none in the makeshift aquarium the others are in. I counted approximately a dozen Triops total. They're hard to count since they move around so quickly. The kids love watching them and I have to remind Martin that he can not touch them because I want them to live a bit longer this time!
MyTriops.com has some lovely pictures and great references on the different species and growing habits.