when to stop the feed

Flushing is a tool to fix a substrate with too high of concentration of minerals. Do you have too high of concentration in the substrate? Changing from properly feeding to starving a plant has other ramifications too. You now are creating a concentration gradient. Cells will puff up with water trying to reach an equilibrium with the fludes entering the plant. If extreme, this could adversely impact cell chemistry. if in soil, you have a buffer of nutes you can let run out. I would simply use trial and error over time as to how long you can go before canopy goes to shit. When you see a hint of fading, that's a good point to start using for length in future. Sucking leaves down is fine, but invovles more effort, more steps etc. probably can't 'see' a difference in growth rate, but also potentially still slowed down since our eyes can't resolve such small differences in addition to a plethora of other relativistic factors at play. in the end it won't make much of a difference... but the key is it provides zero benefit... why do it if it doesn't do anything measurable better? just oversophistication for the sake of sophistication... that's unsophisticated, lol.

Only time you should stop feeding is if you over feed. Reduce feed by the end because your plant is eating less.

I'm with Ezzjaybruh here...