Earliest after flip pollination could happen

as soon as the plant has a pistil that pistil can take in pollen and turn into a seed this is how selective pollination is done you can only pollinate certain buds of a plant to create seeds in that bud and a new strain though this is a breeding method it has to be controlled very well not to seed the whole plant. as the growerr below has stated you will know when a pistil has been pollinated it will got dark orange like the bud is ready for harvest and you will start getting brown pistils alot sooner in the grow like week 3 or 4 its unfortuante and people say its caused by light leaks more than genetics.

white hairs are pollen receptors.. if they exist, it can grow a seed... even a 'preflower' can produce a seed. any white hairs that existed when you found a nanner or sac could potentially be pollinated. The hairs will turn color much more quickly than usual as the first sign.