If you do it, and I think it's fine to do it either way because the side branches will receive more light, then do it early. When the plant is forming it's 5th node it should have enough root energy for a few days of rebounding while still with a weak root system. Remove all the fan leaves except the first two sets of multi-bladed leaves (they're not blocking anything so you may as well keep them). So with 8 total fan leaves you're going to leave 4, remove 4, and the new leaf set should be preset very soon. The side branches should catch up a little bit, and their leaves will fill in where the old fan leaves would have been.
After a few more nodes you can defoliate again, this time including basically any leaf that is above "another" leaf. Leaving essentially only the fan leaves at the bottom of the plant, with a new leaf set just about to pop up. After defoliating twice the branches of the branches should be filling in as well, giving you a very thick and bushy plant. Give it another 3 or more weeks and this plant would make an excellent clone mother for a SOG. If not, you can top or fimm the tops of the plant after it has rebounded completely from the second defoliation for a very even canopy.
Once flowering begins the plant will be very good at replacing foliage. You can feel free to remove anything that blocks a bud site because the plant has been conditioned to replace these leaves. Trying to defoliate while in flower is a bad idea.
If you are concerned why not just try it out on a practice plant. Grow one extra plant, and do it on the side or something, you might be very happy with the results. I got this info from an old dude in Santa Cruz when I started growing, and recently it has become popular among advanced growers in other forums. Most of the people who speak out against this speak only from theory, and not experience. If you'd like to see some evidence I can steal some pictures from this other forum.