Actually, topping is often better. If you wait until the plant is rather large, and lop off 8 inches, you'll end up with 4-5 pairs of good strong side stems to train into a canopy. I don't FIM but I've done a lot of LST/HST. I even did one of each - LST and topping - on a pair of clones, and they ended up with almost identical yield. Topping doesn't slow the plant like it seems it would. At that age it's pretty hard to hold back that explosive growth.
Now I tend to LST clones and almost always top seedlings. Clones have alternate nodes that make it harder to top well.
GT do you root the tops? I have had great success..you end up with a nice cola!..i have 3 tops I'm experimenting on at present..i think 2 might be Purple Haze (+)...muwahahahhahahahahahahahahah ok..DrZiggy is back..
it will finish about a week, week 1/2 later...throw in same bloom room.