Forget a person, need how long?

忘记一个人，需要多长时间？

youdao

I need to know how long, so that I can let my roommates know.

我得知道大概有多久，这样我就可以告诉我的室友们了。

How long实战 - SpeakingMax英语口语达人

What is never mentioned is exactly how long you would need to remain still and how still for this to be a risk.

BBC: Health threat from computer use

Some of the most important information you'll ever need to know, how long your Dad will survive if he gets cancer, your chances of a good life if you have a stroke, all this is out of your hands.

BBC: Cameron's data speech in full

The rest of us need to plan for how we will pay for long term care since most of us will need it.

FORBES: Insurers Are Getting Out Of Long Term Care -- Is It Time For You To Get In?