I really appreciate this example being included.
I am wondering if "One minute ago" should be accepted as correct as well.
I have met several Greeks (in Greece) for whom English is a second Language, and they simply do not use the word "Ago", but are always using the word "Before". e.g. "Before one minute,..."
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"μετά ένα λεπτό"...is literally "after a minute" indicating the time it took to happen and it could also infer the speed at which it happened.*
But if you want the most usual way of saying "something happened really fast" then you'd use...."σε ένα λεπτό" -- "σ'ένα λεπτό".