I have been doing a 5 min backwash in the old configuration simply to avoid drawing down well until flow rate slows to a crawl. A relief to hear that shorter is common if at high flow rates. In the new configuration will have pump from 200 Gal aerator tank running at 20 gpm, but tank refill significantly slower so keeping total under tank capacity good. A short high output run will work. With approx. 1/2 sq ft area(10" diameter 1.5 cu ft media) this would imply flow of approx 12GPM (DLFC 12gpm?). Well water @ approx 40 degrees but slightly warmer if sitting in aerator tank a while)

Also concerned about excessive flow in that I am dumping backwash through septic system. House is in a steep dirt hill(no bedrock until 50' down) and the well head is on the uphill side of house, so dumping in front yard will cause water flow under house. This has already been a problem with storm gutters which I have had to reroute away from house. I suppose I could cut into pipe diverting downspout away from house for backwash water if really important.