I never paid much attention to run time but I would like to.
I have a sta-rite filter, system:3 S8D110. It does not seem to be variable speed.
Looking on the filter, it shows a max flow rate of 106 Gal/min and a filtration area of 53 sqft for a filtration rate of 2 gpm/sqft. I assume flow rate is based on freshly backwashed and charged filter.
I have a 19,000 gal pool. Based on just the flow rate, that would be 3 hours to run through all my water once.
The run time will also depend on my heating needs and how much I want to rely on my SWG. Having said that, based on flow rate alone even 9 hours is enough to filter the pool 3x (!) - but I wanted to check in here and see if those other filter parameters might change this assumption.