The "Day Overide" feature has a couple of functions. first is for applications where the water use is intermittent. The day overide will force the system to regenerate if the gallon capacity is not reached before the DO is reached. It is a great feature for seasonal installations, the system will regenerate itself and keep itself clean during the off season. Non electronic metered systems lack this feature. If water use is consistent and you simply have an oversized softener, you can adjust the DO to 30 days without any problem. For seasonal applications where there is no water use, the DO is often set for 14-30 days, depending on the person programming the system and local water conditions.
You can set the DO in low level programming, simply press the up and down arrow buttons together for 8 seconds, and you will enter low level programming. Hit the regen button to advance through the programming until you see DO XX xx= days between forced regenerations. The DO is reset every time the softener regenerates, some people mistakenly think that the system will regenerate every 14 days, plus the meter initiated regeneration.
The second feature of the DO is the system can be turned into a timeclock system quickly, and over the phone. If the meter stops working and the phone diagnosis shows this, going into low level programming and resetting the DO to 4, will force the system to regenerate as a timeclock until the repairs can be made to the meter, cable, board, or whatever is causing the problem, until the repairs are complete, the system will at least produce soft water.
F6Hawk, you said it perfectly.