Well FYI longerphotoperiods...24/0 20/4 imo create more males.
I veg no longer than 17/7, but usually more like 15/9...after all the longest day of the year is around 15 hours...I have found that do my best to emulate nature is the best policy as far as creating females...and a healthy grow. Now I am not saying you can't use whatever photoperiods you want. I'm just telling you what I have found through my experiment's over time. I came to these conclusion's after much research and advice from growers who knew what they were doing. There is a thread about fem's by the owner of dutchpassion, that I posted a long time ago. I will try to find it, if I have the time. good luck

p.s. Almost forgot...You are right. Some growers let the plant sex, then clone and revert to veg...As stated above, this is a bad idea and unduly stresses the Hell out of the plant, and tremendously increases the chance of hermie's...peace