You will first see small white postals coming from the base of the nodes. This is the pre flower and the sign you are about to enter into true flowering.
By the end of week 1 of flower, you will have intense growth. You will also start to see small formations of buds at the tips. There will be a bunch of pistols starting to show at the tops.
You will want to increase your light intensity at this time.
I hope this helps.