When to start flush

i start flushing my plants at 2 weeks away from harvest date, sometimes they go 3 weeks but when i flush i know that 2 weeks later i will be ready when the plant is ready, feeding just water for two weeks, i have also tried the no flush with great results, i prefer the flush as it is more accepted , so if your plant is at 8 weeks and you start the flush for a good week or two you should be good