This is the third thread on this topic and probably deserves a sticky but anyway here is what I posted on the other threads:

Turnover is the time it takes for the volume of the pool to run through the pump. However, this does not mean that all of the water has gone through the pump. Some water goes through once, some twice and some not at all. It depends on the plumbing, returns, skimmers and drains. To determine turnover:

First, determine the head loss for your plumbing. A rough estimate is to take your PSI from the filter and multiply this by 2.31. If you do not have a vacuum gauge, add about 10' of head for suction head. Otherwise, multiple the vacuum (in. mg.) by 1.13 to get suction head. Add return head and suction head to get total head.

Second, look up the the flow rate from the pump head curve. Usually in the pump manual.

Third, use the formula turnover (hrs) = Pool Volume (gallons) / (gpm * 60)

Also, you should be able to find the pump curve on the Hayward site.