Use lowercase and periods for “a.m.” and “p.m.”

When referring to time, use a colon only to separate minutes from the hour. 

When writing out times, use a.m. or p.m., lower case with periods and a space separating them from the time. 

Example: 2 a.m.; 4:10 p.m. 

Also use noon and midnight, not 12 noon or 12 midnight.​​