that's strange, ssetta, b/c at the end of episode 2228, both Telly and Susan are about to go to bed at night, but the harmonica theme was still used at the end of that episode. Isn't that strange? Then again, that episode's ending didn't show anyone sleeping. Furthermore, after Susan said "Sesame Street is a production of the Children's Television Workshop", she says good night. I think I might have seen another episode in the late 80s where Maria said it's time for everyone to go home and go to bed. I don't exactly know this for sure, but i THINK it still used the regular ending theme.
I think in order for the nighttime theme to be used, someone actually had to be SEEN sleeping, like in episode 1836's ending. Episode 666, the one where the Count counts lights, had the nighttime theme b/c the last street scene showed people turning off their lights at night so they can go to sleep.
Do you know of any other episodes from 1969-1992 that used that regular closing theme, even though it ended at night and someone was about to go to sleep?