For me it really just depends on each animal, if a kit is massive at 6 weeks, I'll wean it so it doesn't suck mom dry of everything she has in her whole body. If it's small I might leave it on even longer. I usually go by less of a set time frame and more of a size and weight. Some babies even seem too small at 200 grams to me, some seem huge. I always hold until I'm sure they've adjusted well on their own away from mom before leaving, usually at least 2 weeks or so. And this is only on anything I KNOW I can't use, other wise I might sell something out that would otherwise be super show quality or a great breeder. I've already sold one like that this year, she hasn't gone to her new home yet and I wish I'd have kept her looking at her now.