YOU SAID:

There was no telling how long they’d been here.

INTO JAPANESE

彼らがどれくらいここにいたかはわかりませんでした。

BACK INTO ENGLISH

I didn't know how long they were here.

INTO JAPANESE

彼らがどれくらいここにいるのか知りませんでした。

BACK INTO ENGLISH

I didn't know how long they were here.