Is the death note 23 days rule inconsistent?
The 23 days rule does not apply to the time of the death but to the time of manipulation. You can manipulate someone e.g. to be a loyal sevant befor s/he dies but all manipulations can't start more than 23 day befor the death. If you give someone a task that takes more than 23 days it counts as impossible and causes a heat attack. But if you write a possible death and a date than it is perfectly fine as long as it is within the normal lief span and you are not too specific about either time or a slow cause of death.