Its taken about 2 months to get them to that size... Though with the heat lately they've done a bit better as long as it didn't go over 82 or so... My second drawer has some about that size that have only been growing about a month.. I recently changed my mix with them and its stopped some of the cannabilism I was getting of the beetles. I use ground dog food, ground rabbit pellets, dry milk, potato flakes, and ground cereals (I had a couple boxes of stale Kix on hand that I used this time around). For my moisture sources I use greens and veggies. Mixtures of them.. Romaine lettuce, some corn, collard greens or turnip greens. It mixes up the vitamins they get so they get a wide variety of them.