The more nodes you have at the time you FIM the bushier your plant will be. I wait until the plant is about 12" tall with at least 5 nodes before FIMing.
i read in the FAQ (imagine that), that you need at least 5 internodes to FIM, but in the same article it had a 3 internode fimmed plant... its ultimately up to you.
I agree. I fimmed my plants at the 4th node at 8 inches. She bushed out wickedly and with out JOGgin would have been about 3 feet tall. I wished I didnt fim however. try jogging you may like the results.