When night settles on the world of Aeyr the mist will rise and this allows daemons, undead, and other eldritch creatures to walk the aeyrth. The civilized folk of Aeyr have learned how to use protective magic wards to keep them and their property safe from attack at night. However, you don't want to be caught out in the open with no wards to protect you. At daybreak comes respite from the monsters, as sunlight will destroy them with an unquenchable fire, this is known as the Ban. However there are creatures immune to the Ban. Orcs and goblinkind, dragons, kolbolds, beastmen, and others suffer no effects from sunlight, although they typically don't like it.
Western armies fighting each other have been known to stand together against daemon assault when their battles carried over into dusk. Smart generals will ward their camps at night. However, many generals will send out assassins and spies at night in the hopes they can slip through unnoticed by both daemon and men and carry out their dire work. All this being said it's rare to spot a daemon at night, but they are there and you never know if they are watching or hunting you.