To the best of my knowledge, you should repot as late as you need to. Usually 2-4 weeks of rooting should be long enough. Anyways you should always repot as soon as the plant needs it. If you have your sprounts in a 8-16 oz. cup you should repot prob. two weeks, but a sure way to tell is if they have their first set of true leaves, that means about 4-6. Anyways I'm a newb so don't count on only my advice.