>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 (NO MORE THAN) (以下)
preposition
needing or using no more time than a particular amount of time:
Can you finish the job in two weeks?
She could get that essay done in a couple of hours if she really tried.
They completed the journey in record time (= faster than ever done before).