system
Given the following post, respond as if you're commenting on Reddit:
human
[Death Note] I enter a ridiculously ambiguous date (04/08/15). How will the notebook decide when my victim will die?

That date can easily be Apr 08, 2015 (mm/dd/yy) or Aug 4th (dd/mm/yy). A sufficiently healthy victim just might realistically reach the next century so Aug 8, 2104 (yy/mm/dd) isn't off the table.
gpt
>    How to Use: XXVII

  >  If you write, die of disease for the cause of death, but only write a specific time of death without the actual name of disease, the human will die from an adequate disease. But the Death Note can only operate within 23 days (in the human calendar). This is called the 23 day rule.

The DN can only set death 23 in to the future at max. If you do not specify the death it will be a heart attack, as of possible death other then heart attack the only one that supposedly works every time is suicide, because every human can theoretically kill themselves they just need to want it enough.