Pool and spa filters are cleaned based upon pressure. Every pool is different there is not a set length of time required to clean your pool and spa filters.
In order to determine what pressure your system is running at, you must have a properly working filter pressure gauge. If your gauge does not go back to zero when the pump is off, gets stuck so that you have to tap on the gauge, or if the needle is jumping around, you need a new gauge.
To determine when you need to clean your filter, you must first clean your filter really well, this establishes a starting point for your PSI. Once you have your filter put back together and your system has primed, take a reading of the filter gauge (PSI), Write this number down and also take a permanent marker and put a mark at the current clean pressure.
When your gauge reads 8 to 10 PSI above your clean pressure (PSI) mark, it is time to clean your filter. Example would be your clean filter pressure is 10 PSI clean, when the filter pressure gets up to 18 to 20 PSI, it is time to clean your filter.