YOU SAID:

I don't know when he's getting here, though.

INTO JAPANESE

しかし、彼がいつここに来たかはわかりません。

BACK INTO ENGLISH

But I don't know when he came here.

INTO JAPANESE

しかし、いつ彼がここに来たかはわかりません。

BACK INTO ENGLISH

But I don't know when he came here.