you can, but sometimes the plants can go a little longer, the breeder gives a suggested flower time, if they say 9 weeks/63 days they are say yes you can harvest at that time, now you grow such strain and 9 weeks is up and you think it can go longer that is up to you and how you like your smoke, i would say keep your eye on things daily by checking the tris, also i would be flushing so when the time was right i would be able to do the harvest.