My plants are from seeds produced by the last plants I grew.
One plant showed its sex after just 3 weeks of vegging under 18/6 light, while the other plant waited a couple extra weeks.
Neither plant had alternating nodes at the time of showing... So I guess that is dependent on the individual.

Those 2 hairlike growths on the main stem at each node are called "stipules". It is from behind these that your pre-flower sex indicators will pop out.

Just keep an eye on the stipules at the nodes near the top of the plant... They should be showing you what's what any time now

Hope ya get some girls!