Most problems are detected when Inform translates the source text, but this is one of the exceptions, a "run-time problem" which emerges only during play.

Timed events can be set off with phrases such as Krakatoa explodes at 11:12 PM. Each such decision requires the story file to make a note of what will be required, and eventually the space for these notes runs out. The limit is set so that twice as many appointments can be pending at once as there are events, so if all else fails, you can make more space by creating more events.