Sand filters require a longer backwash time than a DE filter. Both work by reversing the flow and blowing buildup and debris to waste (or backwash hose) In my personal experience with sand filters, a solid 2 minutes is sufficient. I have heard that backwashing a sand filter for 5 minutes is good. Unfortunately, you'll lose several inches of water if it's backwashed that long. So, a good tip would be (and this is what I do for sand filters). Backwash for 90 seconds. Bring valve back to filter position and run for one minute. Backwash again for another 60 seconds. Should be good to go after that. If you have a "multi-port" valve then there should be a rinse cycle. Run the rinse for 30 seconds after following the above steps.