What actually stops The Hitcher
The badge text is the only first-party rule Dread Forge has published for this threat.
“It settles on you in the dark. Get back into a lit room before your time in darkness runs out.”
Read that text as the whole allowed answer: Unlit space is where The Hitcher acts, and the rule above names the action that answers it. Nothing in the official text gives a number of seconds, a spawn chance or an audio cue, so this page does not invent one.
8,505 players held the THE HITCHER badge at the last reading, which tells you the encounter is common enough to plan for and rare enough that most players have not solved it.