I don't know how much calcium that product has in it. I see that calcium carbonate is listed as an ingredient, so I would be concerned. Too much calcium can cause bone deformations or kidney damage in growing chicks.
You can use coarse sand as grit. Don't use that fine smooth play sand. That is too small to work but look for rough irregular-shaped grains of sand, like construction sand. For my chicks in a brooder, I go to my gravel driveway and scrape up some finer pieces. If your roads were salted due to ice, this may not be a good idea. Chickens cannot handle a lot of salt.
I usually give mine grit the second or third day in ther brooder. As long as all they eat is prepared chick starter, they really don't have to have it, but I think it starts their system operating the way it is intended to. I just put it in a separate small plastic yogurt cup wired to the side of the brooder. I wait until they know what their main food source is and I don't give them a lot to where they can pig out on it.
You can start giving them treats any time after they have grit. I usually don't that much, not because of any reason not to, I just don't. But mine are prepared for the next time my wife stuns a wasp and puts it in the brooder to watch them play keepaway, or a bug wanders in their brooder, or if they eat something they need to grind up to pass through their system, like larger chunks of wood shavings.
I usually give my chicks baby chick grit (Manna Pro) on day three. I sprinkle it like salt on top of their food once a day. It is red, so you can see how much to sprinkle. A tiny bit is enough. I too agree that it is necessary to jump start their gizzards, and treats are fine any time after that. My babies don't go much for treats until they are a bit older. I give them oatmeal and eggs sometimes if they need a boost or I feel motherly. I tried to sprout them some wheat, and they had no idea how to eat it. Must need a mother to tell them it is good? The hens jump right on that though. I love how when I put my hand in the brooder, the now 6 week old chicks come running as if I have treats. I give them a bit of cracked corn and wheat to scratch around for. HenZ
I put a pie pan of rough construction sand in with them after day 3 or 4 so they can pick out the pieces the right size for them and they can dust bathe in it too. Once they discover how much fun it is they usually about empty the pan every other day.
Treat wise I feed chopped up spinach for the first two weeks then real little criickets or meal worms for another week or so. After that any thing they can fit in their faces. Corn, peas, bread, same as adult birds.
I used Chick Grit for mine. You can buy it at the feed store. If you don't have many chicks, a small bag will last a long time. They don't need it for their chick crumble. Only it they are getting something other than that, that they would need "teeth" for. I felt most safe purchasing this as I knew it would be the correct size and did not have added calcium.
We use Chick Grit too. The chicks love it! If they're on starter, they won't need it until they are off starter. But if you are offering them treats, then start offering them grit at about age 4 days or so. We sprinkle it on the brooder floor so they can scratch and peck for it, like outside, and we also leave a little dish of it near their feed so they can get used to having the two nearby (for when they're out in the coop and they have a hopper of oyster shell and grit).
That stuff that you bought is made by Hartz. NOBODY should be giving their pets anything made by Hartz. They are bottom of the barrel as far as quality. What kills me is on the box there is a cockatiel and a parakeet and neither of those birds need grit! No telling how many people kill their birds because they assume its safe.