You should be able to do that in a mod, as a mod can edit any GUI files, and can also call GUI-exposed functions. Thus call the saving function.
But I think it would be better to have this feature directly in the main game (as an option) than in a mod. You will have to touch files that aren't optimised for modding, which means you'll have to copy a lot of code to your new mod (code that you will need to maintain as the game evolves).
If you want to implement this, start in the GUI files that handle the saving of games, see what functions they use, and try to call them from a timer in the GUI somewhere.