>少なくても試験の英文和訳、和文英訳においては、「3分後に」「2週間後に」というときには、in three minutes、in two weeks をご使用下さい。
英語の世界ではそれは誤りです。
Cambridge Advanced Learner's Dictionary
http://dictionary.cambridge.org/define.asp?key=39636&dict=CALD in (DURING) (期間)
during part or all of a period of time:
We're going to Italy in April.
Some trees lose their leaves in (the) autumn.
I started working here in 1991.
Life in the 19th century was very different from what it is now.
Bye, see you in the morning (= tomorrow morning).
She was a brilliant gymnast in her youth (= when she was young).
How many civilians died in the Vietnam War?
This is the first cigarette I've had in three years.
I haven't had a decent night's sleep in years/ages (= for a long time).