It varies from strain to strain. Sativas are usually larger, slower maturing plants than indicas. If this doesn't answer ur question please be more specific.
plants are in seedling stage till the first full leaf fan shows. say at least 5 blades on a leaf. till it shows that 5-7-9 fan it is still in seedling. and some strains due take longer to show that maximum number. and there is a lot of other variables that keep a seedling in that stage. mine are still in seedling stage but i am growing soil-less for the first time and did not add nutes and had a nitrogen problem; not enough. compost (organic) has hardly any nitrogen at all to start with so mine are stunted but are coming out of it..hopefully.
but it would vary from 4-6 weeks to as long as 7-8 weeks till the full bladed leaf shows...generally. please don't shoot me if i am wrong.