This is a song by the well-known pop group Chicago. The title refers to a time of day, 3:35 AM or 3:36 AM. Lamm himself says that "the song is about writing a song. Its not mystical." Many has speculated about a deeper, maybe occult meaning in thetitle but this is not so.
The solo (originally performed on guitar) can be played by a part 6 player and a part 3 player, but one of the sections of solo may also be omitted.