Sunni ban me or I won't stopn here to help people I know what I'm doing I don't care what a couple of forum trolls think they know your site is really not helping anyone
because it gets completely rid of dissolved solids they are still there slightly not all of it comes out of your containers watering correctly and letting it run out with the 25% runoff
What medium are you in? Noone can really answer that question correctly without knowing what you are doing first.
If you are in peat or coco or a soilless mix. I'd flush for minimum of 7 days, prefer 10-14 myself. If your in soil you can do the same.
Flushing is primarily important when your roots are in a soilless or soil based medium that has heavy salt, nutrient build up which you want to get out of their so your final product burns and tastes better/smoother. Since hydroponics your roots arent effected by sitting in and constantly absorbing salts and nutrients that are built up in the containers it is as important to do a long flush like growing in other mediums.
So, If you are growing in a hydroponic system I would just cut back all nutrients in half 2 weeks out and than just ph balanced water for the final week.