This is a Main Menu command - it should be typed when in the game's main menu (similar to 'developermodeon'), not into the developer console. Typing this into the main menu will enable Vegetarian Mode, which makes it so that enemies only spawn at nighttime. Type vegetarianmode into the main menu again to disable this mode.
The syntax for the vegetarianmode command is as follows:
Search our database of 109 The Forest commands...That Sounds Perfect!