I've thought about doing this to lengthen the life of the motor in a canister filter. The maximum time I would shut it off is no more than 30 minutes so that the bacterial environment in the filter doesn't start to change. This is more critical in the winter b/c of temperature changes if your canister doesn't have a heater. You also have to consider how your particular filter will react to being shut down and starting back up again. Some filter will make alot of noise for several minutes which can be annoying; some may not start up consistently, and that will also affect the bacteria. If you really want to turn off the filter on a timer anyway, I would suggest doing 2 periods of 30 min. each, spaced at least 3 hours apart; and during the day only. Make sure you monitor the filter to see how the motor reacts w/the new routine. With that in mind, decide for yourself if it's worth it to shut the filter down and lengthen its life a little, or keep it on and live with the noise. Noise wise, if it's a vibration issue, you could get a 1/2-3/4" piece of memory foam and sit the filter on top of it to dampen the vibration. If it's an impeller noise issue (inside the canister), try getting air out of the canister b/c most of the time it's that or try replacing the impeller if it's old.