Don 't wait... Because you don't know how long it will take.

不要等待，因为，你不知道等待需要花费多少的时间。

youdao

I don "t know how long it" ll take before the management talks to him about it.

我不知道还要过多长时间经理就会找他谈这件事。

youdao

I haven 't been to a cinema for I don' t know how long.

我都记不清楚究竟有多久没看过电影了。

youdao

We don't know how long it takes to do x 2.

我们不知道要多长时间。

麻省理工公开课 - 计算机科学及编程导论课程节选

But I don't really know about how long it would take people to hack, like, the general firewall

但我不知道人们具体要用多长时间才能穿过防火墙，

理想是当密码专家 - SpeakingMax英语口语达人

What's important about the construction of St. Petersburg-- I don't know how many of you have ever been there; I haven't been there for a very, very long time-- this city is not like Moscow at all.

那么修建圣彼得堡到底有什么重要的意义呢,我不知道你们之中有多少人去过那儿,我并没有在那个地方逗留过很久,但这座城市和莫斯科完全不一样

耶鲁公开课 - 欧洲文明课程节选

But given the state of music-buying, I don t know how long this idea of making an hour and a half of music, in one thought process, is going to survive.

NPR: Mick Jagger: A Stone Alone

If somebody just drives up into your driveway and you're not home -- you don't know who these people are and you don't know how long it's going to take for the sheriffs to respond.

WHITEHOUSE: President Obama Speaks on Reducing Gun Violence

"A lot of people don't know how long to cook salmon, " Ms. Erickson said.

WSJ: Renee Erickson's Roast Salmon With Saut��ed Radishes and Sorrel Cream