Use numerals for times of day, but spell out the number with the expression o’clock, which is used to designate exact hours only.
If you use the 12-hour clock, write a.m. and p.m. with points and insert a non-breaking space between the time and the abbreviation so that these never become separated at line breaks. To do this in a Word document, first write the time and the abbreviation all together (e.g., 8p.m., 9.45a.m.) and then position your cursor between the time and the abbreviation (8|p.m. and 9.45|a.m.) and press the key combination Control+Shift+Space. To do this in an HTML document, insert the entity in that same position. Also, use a point to separate hours from minutes.
Use noon (or 12 noon) and midnight, rather than 12 p.m. or 12 a.m.
If you use the 24-hour clock, use a point to separate hours from minutes. Do not use the symbol h.
When using a.m. or p.m., avoid a leading zero.
If you use the 12-hour clock, write a.m. and p.m. with points and insert a non-breaking space between the time and the abbreviation so that these never become separated at line breaks. To do this in a Word document, first write the time and the abbreviation all together (e.g., 8p.m., 9.45a.m.) and then position your cursor between the time and the abbreviation (8|p.m. and 9.45|a.m.) and press the key combination Control+Shift+Space. To do this in an HTML document, insert the entity in that same position. Also, use a point to separate hours from minutes.
 | The library closes at 8 p.m. |
| The lecture starts at 9.45 a.m. |
| The secretary’s office hours are from 8.30 a.m. till 2 p.m. |
| The Rector’s speech will begin at four o’clock. |
Use noon (or 12 noon) and midnight, rather than 12 p.m. or 12 a.m.
| The tutorial, which was due to begin at noon, began at 1.15 p.m. |
| The campus copy shop closes at 12 noon. |
| The faculty bar will serve coffee until midnight. |
If you use the 24-hour clock, use a point to separate hours from minutes. Do not use the symbol h.
| The meeting is at 18.00. |
When using a.m. or p.m., avoid a leading zero.
 | 08.30 a.m. |
| 8.30 a.m. |
Recommended citation:
«Time of day» [en línia]. A: Llibre d’estil de la Universitat de Barcelona. Barcelona: Universitat de Barcelona. Serveis Lingüístics. <https://www.ub.edu/llibre-estil/criteri.php?id=2380> [consulta: 16 abril 2024].