The phrase is an exclamation marking the event that the user needs to take a massive dump, often one that is minutes or even less to where shit hits the fan, quite aptly.

It's origin stems from the "T minus ____ seconds/minutes/hours etc.." announced for important events, such as New Year's ball dropping, bombs going off, or in this case a shit-storm.

When T Minus is yelled, followed by a time for more accuracy, it is imperative to get him/her to the nearest restroom or else all hell will break loose, or just their bowels perhaps.
John: "Shiiiiiit, T Minus! That Chipotle definitely ain't sittin' well."
Frank: "DRIVE FASTER MATT! We can make it to that 7-11's bathroom in time!"
Matt: "Man, they're gonna need a new toilet soon."
John: "I... can't breathe.. Frank.. if I don't make it, tell my family how I died.."
Matt: "You're gonna be OK! Stay with us!"
by Gnarsauce April 27, 2010
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"T minus zero" means "out of time."

This comes from a countdown convention used in by both the American military and NASA.

Generally, it is used when counting down to a major event that will happen at a specific time.

Mathematically, T is time, minus whatever amount of time is left until the event happens.

If the News Years ball is dropping in 10 minutes, one could say "The ball is dropping in T minus 10 minutes and counting!"

Therefore, "T minus zero" means that there is no time left.
I was working on my term paper all night for my morning class, and all the sudden I looked up at the clock and realized I was t minus zero.
by HanClinto May 11, 2004
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The termination of a countdown. Afterwards, time is denoted by 't plus <amount of time>'
We are at t minus zero. We have ignition and liftoff.
by pythonspam May 13, 2004
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At 1000 to 1 odds of winning, choking when the “game” is on the line.

When the contract was on the line for the next generation space launch vehicle, the first static rocket motor test to clinch the NASA contract was stopped at t-minus 20 seconds to test fire for hardware failure.

Similar experiences include: 2004 New York Yankees in the ALCS, 2008 New England Patriots perfect season, 1980 Russian Men’s Olympic Hockey team, Chris Webber 1993 NCAA finals, the Death Star . . . twice, Michael Vick’s life, etc.
Boy those 2008 Patriots sure t minus 20ed it in the Super Bowl.
by rocketman4life September 2, 2009
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What Mission Control in the Houston Space Center never says. They stop after T Minus 1 because T Minus zero is not significant in the countdown.
T Minus 5,4,3,2,1,0...o theyre already gone!
by Will May 13, 2004
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it means "now". t=time... minus zero..
t minus 20 would mean 20 minutes from now, assuming time was like a stopwatch counting down.
by Bethany Nolan May 13, 2004
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