We tell you to leave Licefreee Gel on the hair for at least 60 minutes to make sure that all the lice and nits are dead. You should leave the gel in while you comb out the nits. You will want to wash it out afterwards so that the gel doesn't dry on the hair as this will make combing / brushing the hair difficult. This is also why we include a shower cap, to keep it moist. There is no reason to leave it on longer than 60 minutes as this will not increase the effectiveness.