after about 4-5 weeks of veg you can look for male preflowers and get rid of those plants
or if you start seeds on 12/12 photo period you could see male signs within 3 weeks
it is quicker to sex the plants by spotting the males first and assume the rest that do not show preflowers are female until they show otherwise
no signs of preflower after 5 weeks (1.5-2ft high) is a good sign and the plant is almost certainly female once flowered on A 12/12 photoperiod this will be confirmed in around 7 days when female flowers (pistils) will show
the time frame of 5 weeks is more about the average development of the plant at 5 weeks or its level of maturity around 1.5-2ft high , with many sets of branches
if the plant is not healthy and has not matured/grown to this level it will not show signs of sex until it has reached this level of growth/maturity during the veg period
male preflowers
peace