well no they don`t show sex till they flower
people think running their lights 18 to 24 hours means the plant is in "veg" ok they don`t flower much but most strains will start the flower after node 5 regardless of lighting times just normally the flowers are very tiny and develop very slowly some people even grow pure sativa`s with 27/7 blue light and take a year or more to finish them just because that`s the flowers they like best, normally there`s no profit in flowers like that so only the person growing them enjoys them