Pat,
The factory setting is for the electrical polarity to the cell to reverse every 4 hrs of operation. For water chemistry levels that are considered "balanced" according to the saturation index, there should be very little incidence of scale formation. The reversal of polarity changes the nature of the pH along the blades in the cell. Where scale builds up on one side of the blades, the opposite side of the blade has a low pH and descales the calcium. Balanced water can afford to switch to the LONG cycle, or on the Digital, it's the 8 hrs reversal.
What this does is allow a longer period of time before the polarity reversal, which increases cell life. However, keep an eye on the cell weekly, so that you can assure that scale is still not building up on the cell. If it stays clean, your cell life will be extended. Then you can switch to monthly visual inspections of the cell.
Hope this helps.