Lice lay nits (eggs) close to the scalp and they will hatch within 7-10 days. If you see nits several inches down the hair strand they have most likely already hatched. If you see nits but no lice crawling in your hair, then the nits may be dead and you may not need to treat again for head lice. These leftover nits can be removed with a nit comb to be safe.