Well okay, to satisfy your curiosity: The longest I've played was on one sunday. I started playing LF3 at about 10am and stopped at about 11pm. Just had some short breaks for toilet or fetching some food. That was not my best idea though. Couldn't sleep afterwards because in my dreams I still ran around and fought monsters. Pleased now?
Yeah, this you like, evil as you are! I can almost see your eyes sparkling while a pair of red horns is growing on your head and there's something coming out of your mouth that sounds like Ehehehehehehehe!