I have the same confusion. Rachio: the problem is the check mark you place next to the number as it is entered. It is different from the symbols next to all other (unmodified) settings and it begs to be touched to enter/validate the new entry. There is no place on the advanced setting screen to save settings.
The answer you gave amounts to user training about how to overcome a poor UI. It works but many more users will follow with the same confusion until this is fixed.