without anyone knowing (when i lived with people) about 2 days.
story: when i was in college i was talking to this chick online (aol chat back in 1999) and went to her house. i left late at night and was gone the that next day and the day after and came back later that evening. my house mates were asking where i was... but it was a good time
when i moved back to PA about two years ago, i would be gone for a week or so going to different friends places, AC, etc.