from what i've heard from credible sources it was started when college kids were trying to find a time to get together and smoke that fit all their schedules...they came up with 4:20 and it spread like wildfire and many rumors of why it had anything to do with weed came along withit....one of the more well known by me (and th is whole area) is that it's t he time when most people light up (which would make sense if you think about the fact that alot of people get off work and out of school between 3-4)