YOU SAID:

once the train leaves the station you've missed the boat

INTO JAPANESE

列車が駅を離れると、あなたは船を見逃してしまった

BACK INTO ENGLISH

When the train left the station, you missed the ship

INTO JAPANESE

列車が駅を出たとき、あなたは船を見逃した

BACK INTO ENGLISH

When the train left the station, you missed the ship