I'm about to do my third harvest so far and two of these plants are a bit weird. It's soil with a drip system, I am using flower nutrients at 2/3 strength. HPS 12 and 12. Plants are 42 inches tall with around 13 tiers each. Six weeks into flowering. The top buds hair's have all turned orange but the buds at the bottom are still solid white. Is it safe to trim my finished buds and leave the others to finish their process? Or.. Should I wait and harvest the entire crop at one time when the slackers catch up?

Well, if your six weeks into flowering then I would say you have some time to go.
Yes, the top buds will mature faster then the lower ones.
As far as the orange hairs go, that's not a definite sign the flower is ready.
In actuality, it's not the hairs we are trying to smoke.
It's the little crystals (trichomes) we are after.

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So as far as my situation that answers the question. But I'd like to know if any one has done intermittent harvesting, such as top of the plant at week 7-8 and the bottoms at 8-9. Just to allow the lower buds the ability to mature longer.

yes dude its perfectly fine to do that. chop the part that are ready and let the rest ripen up.

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