YOU SAID:

My first mission was at 1:00 that day.

INTO JAPANESE

私の最初の任務はその日の1時でした。

BACK INTO ENGLISH

My first mission was one of the day.

INTO JAPANESE

私の最初の任務はその日のうちの1つでした。

BACK INTO ENGLISH

My first mission was one of those days.

INTO JAPANESE

私の最初の任務は当時のうちの1つでした。

BACK INTO ENGLISH

My first mission was one of those days.