Hey,
Reading that paper put out by rx green is a good place to start.
https://www.rxgreentechnologies.com/rxgt_trials/flushing-trial/
However, take the results with a grain of salt as the test was performed on too few plants to be conclusive. They derive that flushing has no effect therefore feeding has no effect. Personally, trusting these results, I believe feeding in the last two weeks only wastes your food.
Hope this helps,