that's very hard to say, it varies depending on alot of factors.
in my tank i took early-stage leaf bases from different species of crypt and planted, mid light good fert and co2. it's been about 3 weeks and none of them has formed a new leaf base, they've grown alot though.
before i rearranged my tank, one of my crypts had 30-40 leaf bases after about one and a half years of growing freely, it was massive.