YOU SAID:
The train left the station on 3 am
INTO JAPANESE
電車は午前3時に駅を出発しました
BACK INTO ENGLISH
The train left the station at 3 a.m.
INTO JAPANESE
電車は午前3時に駅を出発しました
BACK INTO ENGLISH
The train left the station at 3 a.m.
That didn't even make that much sense in English.