L4D2 Level Design/Wandering Witch
From Valve Developer Community
In L4D2, we discover that witches sit and rock themselves only at night. If there's sunlight, they wander. You can control this in your map from the Map > Map Properties... menu item.If you change Time of day to any time of day when the sun is out, including "
Morning", and "
Afternoon", witches spawned by the Director will wander.