Is there any limit or maximum number of days, or is it until you get one of all the endings?

ps: the game's atmosphere makes me feel... weird 

As far as I know the game just becomes monotone after some time, no new dialogues, encounters, or chances to get most endings, but no sudden "game over" screen. Also this is a game about a dystopian future, so it's only natural for it to be rather unsettling.

This means that the game is still a work-in-progress, not really finished yet, and we can only wait for the game to be completed.