Since your using a soil less mix, I would follow the chart you have.
How close are they to finishing? If your close...then the leaves are eating themselves and that's normal. I'm betting xlr8 can tell you more.
Yoo whoo xlr8, we need your in put!
Sorry, I've been crazy busy and haven't been on the forums much last couple of days... but here I am!
Well, I'm not 100% sure on what's happened with the leaves, but the high temperatures you've had are probably a big part of it. The leaf tips look like nutrient burn, which could be in part due to a salt build up as SS mentioned. The other thing to consider is that when the temps are that high, the plant can't take in nutrients as well, and it doesn't take as much to have a nute burn or nutrient lockout situation. Also, sometimes near the end leaves start to die naturally as they'll use themselves up to keep the buds healthy. When they are mostly dead, I remove them, no matter what, to avoid any problems with decaying leaf matter (like mold, certain bugs, etc). Environment is everything with plant health, and I'm sure those high temps you've been having are really behind the sad looking leaves in one way or another.
Having said all that, I'm with OMM, and I would just harvest now. 30% is about perfect as far as amber trichomes in my opinion. There are other factors to consider, but you're good to harvest right now if you want.
Ideally running PH balanced water with no nutrients for a week or so first (flushing) would help remove built up nutrients (would help with plant health, and would also remove nutrient taste prior to harvest).
BUT -- In my personal experience, bud flavor can still be very good without a flush at the end if they are dried and cured properly. The leaves, in my experience, seem to hold more of the poor taste left over from nutrients not being flushed, and I cook brownies/make canna-oil with my trim leaves, anyway, and this isn't an issue for me (not sure what you'll want to do with trim leaves). I still flush when I can, but I've had to harvest without it and had great bud still.
If your humidity still gets up to 60% or higher at times, make sure you keep a lot of air movement in the room where you dry your buds to avoid mold.
Sqwheels - you're almost there and should have a great harvest, and your own home grown meds!