A shroud of legend surrounds how exactly 420 became for stoners what 666 is for satan. Some say it was the time of day when Jerry Garcia died, some say it's Hitler's birthday, some say that 4:20p.m. was when this one group of kids got out of detention and smoked, and the time just stuck, and still others say that 420 is the police code for marijuana possesion. Despite the differing schools of thought on the origins of 420, it is undisputably the optimum time of day to get high. It is exactly half-an-hour after the last daytime class, and provides enough time for stoners to gather in designated rooms and locations to light up a joint, bowl, or bong. On rare occassions, an observer can witness a phenomenon known as 'hot-boxing,' where a large amount of cannabis smoke fills a room or a car full of stoners.
April 20th is the international stoner holiday. While most people might not notice it, a significant minority may be missing from classes or work on this Day of days, presumably to smoke bigass bowls all day long. The day is also a significantly active day for the otherwise sedate NORML, who traditionally pass out hemp ribbons and pamphlets regarding marijuana legalization. NORML, who got their club charter on April 20, 2006, also sells brownies, though at $1 apiece, they are merely symbolic of magic brownies.
Date-Time Convergence Theory
If both of these events are cause for smoking copious amounts of pot, then the intersection of both the date and time is a truly legendary event. Every 20th of April, at 4:20 PM, a massive congregation of stoners leave the safety of their rooms to gather at a hidden location, and smoke up in an enormous circle of communal pieces and the dankest shit. On 4/20/2007, 64 people came together at 4:20 to celebrate.