why, then other games if they wrote that the date is at this time, then it immediately released? there some rule about 18+ games?
If they wrote the date and it was immediately released then, then one of two things happened;
1) They had the game done and ready before the release date listed, so they were able to send it to Steam, and they reviewed it and approved it as well before that time
2) They're with a big publisher or a well known brand, and therefore didn't need to get reviewed
NSFW games do get more scrutiny though, for obvious reasons.