no farther than 3 weeks..... try get a good set about a week in, and a few more here and there a little less than a week later..... that would be to lollipop your scrog for optimum top yields, the idea being to also increase yields by allowing 3-5 branches down around the base of each main cola to develop as well, as they will add a few more nodes during the initial stretch during the first two weeks of flower, and stretch that little bit more during the 3rd week, (with some strains, the lollipop trimming stunts flowering stretch
) the light will be penetrating between the main colas to the lower bud sites you leave un trimmed allowing for optimum use of your light energy....... I hope that makes sense......
oh yeah.... and around the edges of your SCROG..... if you moved your mylar closer it would get that much more Dense light, and if you added some supplemental side lighting, it would get even that much more usable light....... HPS comes in 100W varieties...... I have been looking into the different bulbs and mini ballasts that are available, just haven't quite found what I am looking for yet.....