Threads from God89 said:

When is the best time to "top"? ... I just topped my two 6" seedlings right above the 5th node .. nervous as hell to do it tho.  It's been years since I've plucked a top... I don't cut mine.

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For the first topping, I waited until there were 5 nodes, then topped above the third.  The idea is to let the plant have a good head start in growth, and train the bottom of the plant to be a solid base. 

Here’s a before and after from last year, and the reference I used on how to count nodes.
One thing I did different this year is not trimming off all the leaves (compare the mint smash above to this example), whichever you decide to do just make sure to trim off the new shoots growing out on the lower two nodes so the energy can be directed to the 2 new mains.




Then when the two new mains are long enough, tie them down and wait until those have 3 nodes.  Top above the first node:



Repeat, tie down, wait for 3 nodes, top above first:



Eventually you’ll have 8 new mains coming in nicely.  I read if you grow outdoors and have the space, theoretically you can repeat until you have 16, or even 32 nodes.  But I stop at 8 and have had some good success.

Tie down and defoliate as needed, eventually you’ll have 8 colas full of fat buds:





One thing to note, when you top you can use the cuttings for clones: