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TIME OF DAY

DAY Use figures before a.m. and p.m.:

7 p.m.
the 7 a.m. plane
a four o'clock snack
4:30 in the morning
8:35 p.m. eastern standard time
8:35 p.m. ET, or 8:35 EDT

eleven o'clock
noon (avoid the redundancy 12 noon)
midnight (avoid the redundancy 12 midnight)
four in the morning
7:35:10 (if seconds to be indicated)
Military time:  Use four numbers and no punctuation for military time:
            0600
            1900 hours

See also a.m., p.m., midnight, noon.