Umm, make sure the floro is really close to the plant. (like 1 inch with a fan blowing on it). If it's a few inches already I'm hoping that it didn't stretch.

As for the sexing, people usually get preflowers around days 25-30 (i never got any myself) or within the first week or so of being put into flowering mode.

18/6 is what most people use for veg and 12/12 is for budding.

Little tip tho. Be very patient in letting it veg. The longer you veg the better.

Goodluck.