24-Hour Comics Day is an event held around the world which challenges writers and artists to create a full 24-page comic in 24 consecutive hours.
This dare was introduced by Scott Mc Cloud in 1990
More information at 24hourcomicsday
Of course you can do this dare any day you want - but every year (usually in October) there are organized challenges over the World - check twitter.com/24hcdgr
This Year 2012, it's October, 20th.
Note this dare will push you to the limit (both physically and mentally) - after you get the topic you'll have to invent a story, write the dialogs, then draw 24 pages continuously - and to tell the truth in the end, you will feel very shaky, delirious and probably hungry. But the feeling of having made a full 24 pages comics is overwhelming.
Some 24h comics samples :
http://www.sarahgasser.ch/index.php?/comic/24h-comic/
http://herebemongoose.blogspot.com/2010/03/happy-easter-bunnies-story.html
http://letsgetadditives.blogspot.com/2011/10/curse-of-24h-comics.html
http://24hcomicinstudiokamsterdam.blogspot.com/
http://12forever.blogspot.com/2010/03/24h-comics.html
http://www.lulu.com/shop/search.ep?keyWords=24-Hour%20Comics
A special mention for this guy (Alec Longstreth) - who has made it 10 times!
http://www.lulu.com/shop/alec-longstreth/24x7-a-decade-of-24-hour-comics/paperback/product-6515737.html
Impressive!
Final note it seems that the French have done better ... http://23hbd.com/