Thats not how I do it, but you know about opinions and assholes...
What you are attempting to accomplish has an impact on what you do. If you are in a hurry to smoke this harvest, I would personally just harvest a few buds here and there and keep going with the grow. Harvest a few more every week or so. Then do a blind test with your different timing buds and see which gives you the best whatever you are going for. That will tell you when you SHOULD have harvested which you can clock away in the memory banks for the next grow
I personally don't mess with the lighting times like you describe. But if possible harvest in the morning. Theoretically the plant gives off terps all day for pests, communication etc so the highest terpene count should be in the morning. I've never seen any testing bear this out, but I do tend to agree with it.
If you are going to stretch it out (potential for a much more complex plant the longer you let it ripen) you might want to give it some N and stay away from the PK. This will keep the plant alive and green and converting light into all those good things you are going for. Since you are hydro, you can easily flush again at any time. Make sure your root health is 5x5 too, this is when you run the risk of die off or root problems the most. Plenty of O2, frequent water changes, watch for smells and colors.
No hard and fast rules here. I know this is hard, but you need to listen to the plants and forget about schedules and stuff if you want the best possible outcome. The 8-9 weeks quoted on most seeds are there to help the economic feasibility of a large grow (the more you flip the more you make) not necessarily the best time to harvest from a cannabinoid perspective. You could easily push to 12 weeks or more for most commercial hybrids and get a better product, just less of it on a yearly basis. Really up to what you are trying to do.
Also, are all the plants the same? If not, hard to set a tent wide rule on what to do.