As far as staggering a harvest, i've done it before and probably won't do it again. If the tops are so far ahead to warrant it, i'd consider any behaviour that might be exaggerating it. Some difference in ripeness is normal, but if it's extreme, it's been exacerbated by something local cause. Over-crowding of canopy, too much light on top colas, or whatever else is possible.
also, don't expect any larf to turn into quality buds. Staggering will absolutely get you more consistent 'levels of amber' seen in the trichomes and whatever effect is related, but it will not cause any drastic shift in construction of lower buds. An extra week or two won't change their fate... it'll simply get them to the same level of ripeness.
whether that's worth it or not depends on the individual.
---As far as 'flushing' just have to make sure it doesn't die before the lowers finish. If deteriorating too fast, provide some nutrition. It will not hurt the product of the plant. Alive dead. Simple stuff.
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Flushing before harvest is 100% bro science. When the original reasons for it were scrutinized and shown to be false, some just made up new reasons The embarassment of doing something irrelevant for potentially decades is a powerful motivational force. More than a few people will fall prey to the insecurity monster in their closet. The plant has no excretion system to do such a thing. Nothing is getting 'flushed' out of already constructed flower by dumping water on roots.
The scientific community never bothered with this hypothesis, because it's easily ruled out given existing knowledge. I'd bet the lab that did the mineral content testing and bline-taste test did it mostly for publicity to get their name out there. Or, maybe one of them was/is a stoner in their private life, lol.
I will say that some fade can be a benefit, but not necessarily to the product. It does let you know that the plant isn't overfed and whatever negative effects coincide with toxicities in the plant. A slow degredation that in now way is a concern of decimating the canopy before the plant finishes is perfectly fine and possibly the safer way to go. I wouldn't worry about how long or short it is.. and if the canopy ever deteriorates too fast, never be afraid to add some fertilizer at a common sense dosage. It's much more important that the plant continues to function properly up until you harvest. Seems like common sense, but hey... flushing for harvest does sound science-y based on the false pretenses, but it's an imagination land concept in the end.
Plus, it's nice not to have to mix in fertilizer the last week or more, lol...