给他们打个电话，问问他们什么时候来。

Phone them up and find out when they are coming.

《牛津词典》

他们什么时候来这儿的？

When did they come here?

youdao

你知道他们什么时候来吗？

Do you know when they're coming?

youdao

In another sense, they're more willing to entrust the money back to the board of directors to decide on when and whether to pay dividends.

换句话说,他们更放心,把钱交给董事们管,让他们来决定什么时候或发不发股利

耶鲁公开课 - 金融市场课程节选

you can call your friend and ask them when they'll be free by using a "when" question.

你可以打电话给他们，用“When”问句来询问他们什么时候有空。

When 课堂 - SpeakingMax英语口语达人