刚好3分钟／半小时（等等）
exactly three minutes, half an hour, etc.
We managed to get to the station in five minutes flat. 我们设法正好用了5分钟时间赶到了车站。
We packed in half an hour flat and were out of there.
She'd prepared the whole meal in about ten minutes flat.
Honestly, it will take me half an hour flat to clean the whole lot.
They ate the whole pizza in five minutes flat.
You can be in Manchester in two hours flat.
See also: flat adverb (COMPLETELY)