Time

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Calculate with time: seconds (s), minutes (min), hours (h), days, weeks, months, years, including the relationship between units
  2. Calculate times in terms of the 24-hour and 12-hour clock
  3. Read clocks and timetables
  4. Solve problems involving time zones, local times and time differences

Understanding Time Units

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Time is measured using different units depending on how long a period we're talking about. You need to know how these units relate to each other.

Basic Time Conversions

Here are the essential conversions you must memorize:

  • 60 seconds = 1 minute
  • 60 minutes = 1 hour
  • 24 hours = 1 day
  • 7 days = 1 week
  • 365 days = 1 year (or 366 days in a leap year)
  • 52 weeks = 1 year (plus 1 day)
  • 12 months = 1 year
  • 1000 years = 1 millennium

Important: Time does not work in tens, hundreds, or thousands like most other measurements. Instead, it uses 60s and 24s, which makes calculations a bit different from normal number work.

Days in Each Month

You need to know how many days are in each month of the year:

  • January — 31 days
  • February — 28 days (29 in a leap year)
  • March — 31 days
  • April — 30 days
  • May — 31 days
  • June — 30 days
  • July — 31 days
  • August — 31 days
  • September — 30 days
  • October — 31 days
  • November — 30 days
  • December — 31 days

Memory trick: "Thirty days hath September, April, June and November. All the rest have thirty-one, excepting February alone, and that has twenty-eight days clear, and twenty-nine in each leap year."

The 12-Hour Clock vs The 24-Hour Clock

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There are two main ways to tell the time: the 12-hour clock and the 24-hour clock.

The 12-Hour Clock

The 12-hour clock goes from 1 to 12 twice in one full day. It uses am and pm to tell us which half of the day we're in.

  • am (ante meridiem) means "before midday" — this covers the time from midnight (12:00 am) to just before midday (11:59 am)
  • pm (post meridiem) means "after midday" — this covers the time from midday (12:00 pm) to just before midnight (11:59 pm)

Examples:

  • 7:30 am means half past seven in the morning
  • 3:15 pm means quarter past three in the afternoon
  • 11:45 pm means quarter to midnight

The 24-Hour Clock

The 24-hour clock counts all the way from 00:00 (midnight) to 23:59 (one minute before midnight). It doesn't need am or pm because each time only happens once in a day.

The 24-hour clock uses four digits: the first two are the hours, and the last two are the minutes.

Examples:

  • 00:00 is midnight
  • 07:30 is half past seven in the morning
  • 12:00 is midday (noon)
  • 15:15 is quarter past three in the afternoon
  • 23:59 is one minute before midnight

Converting Between 12-Hour and 24-Hour Time

From 12-hour to 24-hour:

  • For am times: The 24-hour time is the same as the 12-hour time (just write it with four digits)

    • 10:00 am → 10:00 or 1000
    • 7:30 am → 07:30 or 0730

  • For pm times: Add 12 to the hour number

    • 2:00 pm → 2 + 12 = 14:00 or 1400
    • 3:30 pm → 3 + 12 = 15:30 or 1530
    • 11:45 pm → 11 + 12 = 23:45 or 2345

From 24-hour to 12-hour:

  • If the hour is less than 12: It's an am time

    • 0315 → 3:15 am
    • 0930 → 9:30 am

  • If the hour is 12 or more: It's a pm time, and you subtract 12 from the hour

    • 1400 → 14 - 12 = 2:00 pm
    • 1815 → 18 - 12 = 6:15 pm
    • 2200 → 22 - 12 = 10:00 pm

Special cases:

  • 12:00 pm is midday (noon) → 12:00 in 24-hour
  • 12:00 am is midnight → 00:00 in 24-hour

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