Flushing is not a normal part of the growing process until the last week or two of the grow. Otherwise, you only want to flush if you accidentally nute burned your ladies. The idea behind flushing is to remove the nutrients. Why would we pay so much for nutrients then regularly flush them out?
You should only flush 1 time. 2 weeks before harvest, it removes any unused nutes from the soil. It's supposed to help with the flavor of the buds. When you flush you should use about 3 times water to pot size. so i you have 3 gal pots flush with 9 gal of water.
Just start using normal water and harvest when they're ready. You should flush at least a week, better to do it for two. Don't let you ladies keep growing way past their best harvest date, though.