A countdown begins as soon as a launch moment is scheduled -- days in advance.
"T" is the exact moment of take-off.
So first we hear that the countdown is at "T plus 5 days"
Then it is "T plus 4 days, T plus three days" etc
It was common to hear "T plus two days and holding," meaning that the countdown had been stopped while some problem was addressed. Once it was fixed, the countdown resumed from where it had left off.
Then finally it is down to seconds: "T plus 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 BLASTOFF!
The next second AFTER the blastoff is "T minus 1."
The next second after that is T minus 2 and so on.
The Apollo astronauts reached the moon at "T minus 5 days."
So the passage means that "One second after the Apollo rocket took off, globalization began."
Saying it was "T plus one" for globalization is a literary device meaning that we can start counting the seconds since globalization began ... starting from that moment in history and continuing until today.
Instead of a countDOWN from one time down to the exact moment something will happen, it is a countUP -- a place to start, and then add and add to its unfolding.
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