You may have to wait till you flip to 12/12 to find out the sex.
I've seen it on the net about people sexing plants in veg, but damned if I can ever see it.
What i normally do is veg them for 2 weeks switch to 12/12 if I see white pistols pop out I no it's female and then put it back under 24 hour light for another 3 weeks.