When do i begin nutes with my clones?

OK i have 5 clones that i have had planted in coco for almost a week under a 600w HPS ligh. They appear healthy with lots of new growth, with the exception of a couple plants have their leaves pointing down. But they still look like they are growing. they are between 3" and 4" tall with at least 8 leaves on each plant. My question is this should i begin with low dose nutes? i know the rule of thumb is 3 weeks but isnt that for seedling? the clones are already much older than 3 weeks. also 1 plant is at least double the size of the other 4 should i not nute her so the others can catch up? oh and i going to grow these SCroG. Any help and advise i can get would be great.

When they begin to appear as if they need them...