Yokai appear roughly in the evening, "Tasogaredoki", and the dawn, "Kawataredoki".

Tasogare and Kawatare mean "Who is that?"
In general, Yokai try to threaten man, so they like it when it is rather than pitch-dark.
Because are doesn't see a person's appearance easily when it is dim.
This time zone is called "Oumagadoki."

However, the apparitions who makes people afraid (for example, Mysterious phenomenons etc.) show up in the middle of the night.
It is the most effective time for them.