Complete Noob
Member
Two weeks before flush is good, as a general rule. However, you're also right about reading your plant, and trusting your own senses. I'd say it depends on the plant. Here's what I mean:
A lot of cannabis plants put on a bunch of their bulk in the last 2-3 weeks of flower. That's when dry kool bloom is crucial, to help put on that bulk and keep 'em green during a time when you're also reducing N and they're likely to start yellowing. Now, if you've observed that the plant you're growing tends to start yellowing earlier than that, feel free to start using Dry KB earlier. Or maybe instead increasing by a little (say, 20%) the amount of liquid KB you're using, assuming you're using it.
If you've observed that you have a plant that bulks up gradually, rather than kinda suddenly all at the end, feel free to start using it earlier.
The feeding schedule is a very, very well laid out set of general guidelines, and is meant to be tailored by you, to your own needs. I think the best course of action is to grow it once or twice according to the directions (unless the plant tells you something's wrong, by yellowing or dying or whatever.)
Once you've got a base of experience with this plant, you can start to dial in specifics with your nutes (like for example, you've learned that it yellows in week 3 if you don't reduce N, aka "A" nutrient. Or, it puts on all its bulk by the end of week 6, so you'll use dry KB earlier.) You can't know these things til you grow it at least once, and there's no way around that.
Good luck, and happy growing!
My buds were getting longer but now appear to be getting wider day by day should I begin dry koolbloom today?