User blog comment:SpiritedDreaming/RWBY Tower Defense Game: Attack on Kevin Take 3/@comment-26397825-20161129122833/@comment-26397825-20161201114312

Then it becomes a case of 'will the game be over in 6 days or 6 weeks'?

Consider that the dragon does 5-15 damage daily, it takes roughly 20-60 days. If we make the cannon do tons of damage but charge for 7 days, then depending on the damage it either kills the dragon in a week or takes over a month to do so.