YOU SAID:

we shall depart at 3:00

INTO JAPANESE

3:00に出発します

BACK INTO ENGLISH

I'm leaving at 3:00.

INTO JAPANESE

私は3時に出発します。

BACK INTO ENGLISH

I leave at three.

INTO JAPANESE

帰らないといけなくて

BACK INTO ENGLISH

I have to leave at three.

INTO JAPANESE

帰らないといけなくて

BACK INTO ENGLISH

I have to leave at three.