To start off, residential pool equipment is sized to turn over a pool's water volume 1.5 times in a 24 hour period. That means that the water in the pool gets run through the filter and any chlorinator ( in or off line) that you may have 1.5 times every 24 hours. When you start reducing filter pump run time, you knock that ratio down. To get all of the pool's volume through the filter only one time in a day then requires 18 hours of run time. When your filtration drops below 18 hours...not all the water gets filtered. Your chemical costs then start to climb to keep that water clear. It's a fine line here. Less than 18 hours run and it may actually cost you more in chemicals than what you save in electricity. You lose. If the cost of electricity in your area is expensive, You lose.
I wouldn't go with less than 18 hours run. You're still saving 6 hours juice which is a 20% saving on your electrical over a 24 hour run but you're still turning over all your water. If you plan on a party..you'll want to increase the run time, if no one is using the pool and it's getting cooler out, you can reduce it just a bit from 18 but not much.
former pool tech