a plant started from seed that is NOT an autoflowring plant will show "pre-flowers" at maturity. As a plant grows, it has or makes nodes, where you see one leaf exactly and precisely across from an other opposing leaf.
BUT when a pot plant becomes a mature plant , an adult, it will make leaves that are staggered, one on one side and one up higher on the other side. In a rapid hydro grow, it will be between 4 and half weeks and 6 weeks.
THEN a "pre=flower" can be seen.
A female preflower will loook like a minature pear, upside down, and two itty bitty little hairs called pistals sticking up from the top.
A male preflower will look like a crab claw, some say like two eagle talons, some say like a double-pear, but the main thing is there are no two pistals sticking up.
AFTER 12/12 is started, in Hydro, (soil is slower) ten to 14 days later, you will see the start of a flower.