seedlings should be started under 12 hours of light and slowly increaased over time just as in nature....seeds that sprout under spring like conditions and lighting have a better chance of being a girl....seeds that sprout later in the year under warmer conditions and longer hours of light have more chance of being a male as they will grow faster and stretch more so that they can drop pollen onto the shorter females to make more seeds to perpetuate itself.

when i grew from seed i always started them in the flower room for at least 3 weeks before increasing the light.....do what nature does not what your friend tells you