Because cannabis is intensivley cultivated and bred it's not unusal to have seedlings from particular strains that do weird stuff because the gene's are not too stable - I had one a couple of weeks ago that came out with thee leaves, each with three blades for the first set and then promptly died - may be worth germming at least 3 seeds to make sure you get a female.

You don't need to let the root get an inch before planting, pop it in the medium as soon as it shows. You would be better of putting them straight into a pot as well as those root will grow FAST.