in soil it's pretty simple : either #1 - three weeks plain water no run off or #2 two weeks plain water with 10-20% runoff, or #3 one week / 10 days watering only with additives like enzymes or chelation agents (humic/fluvic acids) ... the "amber hairs" cant really help you actually, sometimes they turn sometimes they dont, and for sure they all turn after the chop. You really need to time it based on the trichomes, maybe start the flush at 90% milky/full trichomes. If you really need to do it on the pistils then maybe start a two week flush even by the end of next week, one week more plain water wont really hurt. By the way now is a good time to add P/K boosters to get that fat nug with that frost on. Hope this helps ! π