hmm how would i implement it myselfThe "breakfast" checkbox only affects the built-in breakfast activities (which only happen once per day anyway, so you don't need to turn it off if you log back in during the same day).
Any loginScript that you create will be executed on every login. If you want it to do things once per day, you need to implement that yourself. Probably the easiest way of doing that would be to exit the script immediately if your fullness or drunkenness is greater than zero.