The override forces the system to regenerate no less than X amount of days. For residential systems without iron, a setting of 14 or even 30 days is acceptable. I know someone on this site will argue this, but simply put, the 5600 Econominder, the most popular control valve for the past 30+ years does not have an over-ride feature and only regenerates when the meter tells it to, and I have not seen this as a problem, ever. If you have iron, more frequent regenerations become important but a simple chemical cleaning of the resin, or occassional replacement of the resin can also be done.
If your system is sized so that it regenerate more than what you set the over ride, the system will ignore the over ride completely. This function is primarily for applications that are not regularly occupied, vacation homes, etc where the system may not regenerate for months on end, this is not advisable.
If your systems electronics have determined that the system needed to regenerate every 5 days according to your metered water usage, the over-ride is non functional.
The 5600SXT flashes between the time of day and gallons remaining. When it gets low, you will see the "water spigot" on the display start to flash, indicating the system will regenerate tonight.
Hope this helps.