I would let it grow longer, the 7 day rule really isn't very good, it was for CFLs in certain setups but the longer you can let it grow, the better. 10-14 days. I try to never go past 16 days because even with high power LEDs, you can start to see the first signs of detachment.
As far as the changing conditions of the screen I wouldn't get too concerned with this at this point. Things are still settling in, and your tank might be finding a new "set point" so your growth can tend to vary quite a bit from cycle to cycle. What you are looking for is a long term pattern of growth, first step is to get a mature screen and then you can start to see that pattern.
But I like your detailed record keeping, that's fantastic, makes troubleshooting a lot easier.
Regarding screen maturity, this is something that I have been meaning to write up for a while, been rolling thoughts around in my head....here's where I'm currently headed (not a guideline yet)
First 4-6 weeks of a screen are the initial maturing phase. This is where you get the first sprigs of algae attaching, and holes start to fill in - sometimes quickly, other times not so much. When you scrape a screen and 25-50% of the holes stay filled in (before you rinse with water) then you are approaching the end of this initial maturing stage.
During this stage, you should never scrub the screen with a stiff brush, with the exception of the area near the slot/screen junction (which you should always scrub). Just a palm swipe and/or maybe dragging the scraper or credit card across to loosen any poorly attached growth, and a brief rinse. You are really not "cleaning" at this point. Maintenance every 10-14 days, can go every 7 days if your gut tells you to (you are getting full coverage, i.e. cannot see the screen pattern = clean it) but in general, let it grow. But do not start singing "Let it Grow" to the tune of Frozen. You can tank me later for now having that song stuck in your head.
Next 1-2 months: secondary maturing. This is just a continuation of the initial stage, but the screen will now form a better calcification layer (as long as you don't scrub it really hard with a brush all the time!!!) and this will allow algae to get an even stronger foothold. The holes will fill in more and even if growth comes out of the holes after a cleaning, there will still be algae attached to the canvas around the edge of the hole (this is all that really matters, the holes don't have to be 100% occluded to be considered "filled in"). You will be scraping and rinsing the screen, and maybe passing over the screen with a soft toothbrush (in a 'swipe' not a scrub pattern) but still no hard scrubbing, and you shouldn't necessarily need to use the scraper like a chisel, you should still be able to drag it across and remove most of the growth (this may never change for you actually)
4+ months (4-6 week initial, 2 month secondary): your screen should really be rocking and rolling at this point, when you scrape both sides you should have nearly 100% full occlusion of the holes prior to rinsing, and you may have areas that really require you to put some elbow grease into it to get the algae off. You might start seeing funky growth like dark red turf (that looks orange when you scrape/squeeze it) or stuff that is kind of like fingers or nodules (once described to me as a "koosh ball" except with more thickness), some of these will come and go, some will stay and you might need to scrub it off with a stiff brush from time to time (like the red turf) in order to keep the fast-growing GHA in play.
