well, mine showed sex while still in veg, every one of the NL popped a preflower on the 5th internode. I fimmed the big NL right around the fifth internode, which gave me a total of 12 shoots to LST. IMO, when you top should be determined by how many tops you want to end up with. Once you determine that, then it becomes a function of what internode you want to top at and whether or not you want to fim it or not.
For example, if you want 4 tops, then fully top it at the fourth internode, train the top 4 shoots out to each point on the compass, then use the couple spindly shoots on the bottom internode for clones.
If you want 6 tops, then FIM at the fourth internode, if you want 8+ then FIM the fifth internode adn get ready to tie and retie on a daily basis.