音のストリームは効果的か？

>On confirming your payment, I'll get back to you in thirty minutes.
>（振り込みの確認ができ次第、３０分以内にご連絡差し上げます。）

Cambridge Advanced Learner's Dictionary
http://dictionary.cambridge.org/define.asp?key=39636&dict=CALD

in (NO MORE THAN) （以内）
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).