Look at the main stem where the branches grow/sprout from.
When sexual differentation occurs, calyxes with white PISTILS ( also known as primordia/pre-flowers) will form here, 2-3 weeks before flowering commences in earnest.
Week 7 in my diary "cannabis conundrums" has pictures of these primordia, if you are keen to see what to look for.
Just remember, - less leaves = less energy production = less growth!
Heavy defoliation can cause delays with flowering.
Hope this helps, Organoman.