How long is it since we last went to the theatre?

我们多久没去看戏了？

《牛津词典》

How long is it since he left this school?

他离开这所学校有多长时间了？

youdao

How long is it since you left your primary school?

你小学毕业有多长时间了？

youdao

Besides the actual performance, they look at how long it takes the soldiers to complete their tasks, since time can make the difference between survival or death for those who are lucky enough to be alive after the nuclear blast.

VOA: standard.2010.07.21

And while I have long since forgotten how to solve a differential equation, I did learn how to drink responsibly (no tequila shots on an empty stomach).

FORBES: Grownup Training

Memory loss can be a factor, and they may not realize how long it has been since their last bath.

CNN: Is bathing just once a week healthy?

How long had it been since someone massaged her hands and feet?

FORBES: Magic Touch: Six Things You Can Do to Connect in a Disconnected World.