ŌMAGATOKI

Sunset as the hour of meeting evil spirits

Ōmagatoki is the twilight hour between when the sun sets and the sky goes dark. The border thins between sekai — the world we live in, belong to and recognize — and ikai, the “other” world. During ōmagatoki, the evil spirits, yōkai, yūrei and other dark things cross over into our world.

Text from yokai.com/oumagatoki

Watanabe Shotei, Sunset Glow at Tone River, 1924

Implicit reference
Explicit reference

Ōmagatoki is mostly represented as the twilight hour of the day, corresponding to the beginning of the conflicts. However, it's more common that in anime it's characterized by the arrival of strange creatures.