Wow, Eugene, 25 GPG is crazy hard! As for the calendar override, I was quite curious about this and I wanted to learn more, so I have just called your water softener manufacturer in Brookfield, WI at (800) 279-9404 and asked them about this. They said that the calendar override will only trigger a regeneration if it has not regenerated for 7 days. So I don't know why it regenerated on Sunday when it had only just regenerated on Friday. I'd keep an eye on that and see what's going on.
Looking at the manual:
The HE setting uses 3.4 lb of salt and 46 gal of water and will provide 600 gal.
The HC setting uses 16.7 lb of salt and 57 gal of water and will provide 1,360 gal, as you mentioned.
So whichever of the two settings you use, it may well be the case that your softener will regenerate once per week based on the calendar override, so the HE setting will save lots of salt and a little water.
On the other hand, if your water usage is higher, then it may end up regenerating every 5 or 6 days on the HE setting. But in this case the calendar override should NOT cause it to regenerate at all as it will never go longer than 7 days.
Ralph, when I was reading about softeners, I read a piece of advice that said you should never let your plumber program the softener LOL. I bought our softener from a company in Canada and I had a local plumber install it. He made a really nice job of the plumbing and the installation and I was very happy. I asked him if he had programmed the hardness and he sheepishly said, "I don't know what that is." I told him not to worry and that I would do it. But obviously if you have an actual water softening company to do the work, then they should know.
Also, Ralph, our water softener records our water usage in gallons and litres. And our water bill records our usage in CCF (748 US gallons). It appears that almost all our water usage is taking place outside the house for irrigation and only a fraction is going through the water softener for use within the home. In fact, the water bill shows that we have been using just over 1,000 gallons (about 4,000 litres or 4 cubic metres or 4 tonnes) per day. Apparently this is normal in the desert and our neighbours' water usage is not massively below ours, although ours does still seem unusually high. It still sounds shocking to me. I can see why many people opt for "desert landscape" in the desert. Green lawns, flowers, trees and plants may look nice but they sure do need an obscene amount of water to create the oasis in the desert. Fortunately water is extremely cheap in Palm Springs.
Louis, inside the home, we tend to use about two-thirds of what Ralph uses in our homes in Sitges and Palm Springs. It was the same when we lived in the UK, typically around 500 litres per day.