When you’re talking about time zones within your target audience’s country, use these regional guidelines. If you’re talking about time zones outside that region (international, from the reader’s point of view), use 24 hour time with UTC offsets.
New York: UTC-5
Australia, Canada, and US time
Express time as H:MM AM/PM time zone. Include a space before AM or PM, but no periods. Include minutes, even if it’s on the hour (for example, available from 3:00 PM to 4:00 PM). Noon and midnight can be referred to as just that, or as 12 AM and 12 PM.
Abbreviate time zones within Australia, US, and Canada like this:
Pacific Time: PT
Eastern Time: ET
Central Time: CT
Mountain Time: MT
Australian Western Time: AWT
Australian Eastern Time: AET
Australian Central Time: ACT
Use abbreviations (PT, ET) when combined with a time reference (ex.: 5 AM PT).
Spell out “Eastern Time,” “Pacific Time,” and so forth, when standing alone without a time reference.
Note: To reduce maintenance and upkeep, we no longer refer to Standard/Daylight Time.
8 AM PT
11:00 PM ET
3:00 PM to 4:30 PM AWT
Use 24 hour time without time zones (assume everything will be in Brasilia time) and done leave a space between the number and the h. Noon (Meio-dia) and midnight (Meia-noite) can be referred to as just that, or as 12h and 24h.
17:25 (only when in a table, technical use, or departure board for trains/planes)
Use 24 hour time without time zones. (France has only 1 time zone.) Leave a space between the number and the h.
13 h 15
09:00 (when in a table, technical use, or departure board for trains/planes)
13:15 (when in a table, technical use, or departure board for trains/planes)
United Kingdom time
Use 12-hour times with periods instead of colons and no time zones.