Jerry,
I use approx 650 grams of salt and flush for about ten minutes.If you have a high TDS reading you may have to flush more often,
As an example,if the TDS reading of the water supply is 100ppm,the softener resin are able to treat approximately 2250-litres of water....So the resin need to be regenerated every 900-litres of water collected as the ro filter only retains 40% of the total incoming water.
Cheers,Tony.