I'm not a chick expert, but you don't need to wait that long on mealworms or scraps. If the chicks were being raised by a mama chicken, she'd have them eating bugs and such from day one. The sand you have is fine for grit. I asked a similar question about grit, wondering if I actually should buy grit from the store or if the dirt/sand in my yard was okay. I did end up buying a package of chick grit with a "chick package" online and turns out, it's coarse sand! So, yeah, waste of money and the shipping cost was steep! For sand...(my kid has a playground in the yard filled with many, many cubic feet of SAND, plus we have a wash outside, filled with SAND)....total sucker!!!