AsNoriuanswered grow question 3 years ago More experienced growers see plants structure, by week 4 I would put all most lanky and tall away and would concentrate my efforts on bushier plants . I guess first pile will be mostly males if you have good regular seeds, not hermies.
In reality fastest way - take clones and check them from go on 12/12 cycle, it's irrelevant will they make it, you just need them to start showing sex.
Lab is option, but all posting takes time and money ..
Good luck !