Like I pointed out here, the 23 days rule does not work that way. If the time of death is later than the natural one, the natural death will happen. If the time of death is before the natural one, it will either be a heart attack or the specified death.
The death note works for every time of death between the moment of entry and the natural time of death. The 23 days rule just specifies that one can't manipulate the victomsvictims for more than 23 days before their death including giving the victomvictim a specified disease that takes more hanthan 23 days to kill the victim.