twelve o'clock; midnight; noon
Means 0:00 or twelve o'clock in time expressions. In modern 24-hour usage it most often means midnight; 午前零時 is midnight and 午後零時 can mean noon.
午前零時に日付が変わる。
The date changes at midnight.
The fireworks will start once it turns midnight.
Registration starts at noon.
零時を過ぎても電車はまだ動いていた。
The trains were still running even past midnight.
If I don't get home by midnight, the gate will be locked.
The meeting ended exactly at noon.
真夜中 refers loosely to the middle of the night as a stretch of time, whereas 零時 is the precise clock time 0:00.
深夜 describes the late-night period in general, while 零時 names the exact instant of midnight.
Standard kanji spelling, especially in formal or written time expressions.
Attested numeric spelling using a full-width zero; common in schedules and timetables.
Practical half-width numeric spelling, often seen in digital text; equivalent to ０時.
Compound of 零, conventionally used here for zero, and 時, hour or time; the spelling directly reflects the idea of 'zero o'clock.'