Your first grow is def prettier than mine. Been a lurker here since 2009. Soakin' up knowledge and tryin to find my way... One thing I have learned is there are as many different ways, opinions, tricks etc. to harvesting as there are ways to grow.
I have flushed a crop or two and IMHO never noticed a difference in the bud compared to un-flushed bud. Try smokin a leaf or two though and you can def tell the diff between flushed and not flushed. This leads me to my point. I have read here on RIU that the fan leaves and roots store the nutes that the flowers need and disperse them as needed. This does fall in line with my leaf smokin experiment. For me, I do not flush anymore.
I figure God put the plant here, and I will try to give it optimum nutrition and growing conditions throughout its life. Sometimes I have been able to keep the plant green throughout flowering some strains no luck whatsoever. I grow a few small plants for personal use so I probably would not be able to notice if I did not bring the plant to its genetic potential. All I know is when I harvested, I was happy with the results, and learned a few things along the way.
As far as determining harvest time, I use trichomes and calyxes. Some people have suggested getting a 50x loupe or something similar to view trichomes. I went to the drug store, got the strongest $5.99 pair of reading glasses I could get and they work great for me as a magnifier. I like the trichome method as to me it makes sense. As plants die parts start turning brown. Trichomes start turning amber. When things turn brown they are degrading so I imagine as trichomes turn amber they too are degrading. I shoot for just a few amber and mostly cloudy trichomes on different buds and different areas on the plants, that combined with enlarged calyxes and I chop. Could I have let them go another week? Maybe. Would I notice another 1/2% THC or another couple of grams on my smaller plants? probably not. Again this is just my relatively novice opinion. For me this is just a fun hobby with a fun product to use afterward. I don't get hung up on the little things
You have two beautiful plants that are in two different stages of maturity and an excellent learning opportunity. The one with the all white pistols I would guess has about 3 weeks to go or so. The other one I would say is getting close. Get a magnifier and look at the trichomes on both. Compare them, study the sometimes subtle differences between clear and cloudy. Look at the differences in the calyxes between the two of them and you will be able to tell whether the more mature plant's calyxes are swollen. When it feels right chop her down with love, knowing you did the best you could to raise her right. I'm sure you will be very pleased with the results.