I have a list of supposedly 'female beneficial' techniques, from an old grower's guide I came across ... I am NOT endorsing it, just passing it along ... it says:

" start these changes at '3-pairs of internodes' stage, and continue for the next 2-3 weeks " :
1. Higher Nitrogen
2. Higher Humidity
3. Lower Temperature
4. More Blue Light
5. Fewer hours of light (this was to discount the 24-hour lighting argument)

you know what ? ... I have a hard enough time, just keeping plants happy and healthy, than to worry about influencing their gender ... if you grow even close to 'correctly', nature will normally give you at least 50% females ... not a disaster, I wound up with only ONE Willie Nelson female from ten seeds (9 no-germinate) ... but, took over 50 cuttings from it, for cloning ...