Rules of Speed Chess
“From 1990 through 1995 a group of roughly eight chess players, including myself and Willie Speaks, met regularly during breaks at work to play 5-minute speed chess. Lightning speed and keen competition made it necessary to develop a set of rules to settle disputes that occurred during the thousands of games that were played.”
From: http://billpriceweb.com/speedrule.html
The rules as applied are interesting. I read/skimmed - bookmarked - will check out in more detail later. The one with a checkmate but opponent time ran out with stopping that clock but ones own flag fell in the meantime; yet the two sides can agree to a draw or a winner; that could get kinda hairy in some circles.