# Time, Timetables and Time Zones

> Change between 12-hour and 24-hour time, find how long something takes, read timetables and charts, and work across Australia's time zones.

From Selective School Maths on WhizzNotes, free study notes for NSW students: https://whizznotes.com/selective-school-maths/time-and-timetables/. Updated 4 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The phone call to Perth
Ruby lives in Sydney. Her grandma lives in Perth. One Saturday at 8 am, Ruby rings to say happy birthday.

"Ruby, it's 5 o'clock in the morning!" says a sleepy grandma. Ruby forgot that Perth's clocks are behind. In summer, Sydney is 3 hours ahead of Perth.

Next year Ruby works it out first. If she wants to call at 9 am Perth time, she must ring at 12 noon in Sydney.

**In short:** 24-hour time counts from 00:00 at midnight to 23:59, so add 12 to pm hours. To find how long something takes, count up to the next hour, then whole hours, then the minutes left. Australia has three main time zones, and the east is ahead of the west.

## Before you start

- 60 minutes in an hour and 24 hours in a day (see Metric Units and Conversions).
- Reading an analogue clock.

## 12-hour and 24-hour time

- **am** is from midnight to just before noon. **pm** is from noon to just before midnight.
- **24-hour time** uses four digits and no am or pm.

### Key idea: Changing between them
- For pm times (except 12 noon to 12:59 pm), add 12 to the hour: 2:45 pm is 14:45.
- From 24-hour time, if the hour is 13 or more, take away 12 and write pm: 19:20 is 7:20 pm.
- Midnight is 00:00, so 12:15 am is 00:15. Noon is 12:00.

## How long does it take?

### Key idea: Count up in jumps
1. Jump to the next whole hour.
2. Jump whole hours.
3. Jump the minutes that are left.
4. Add up the jumps.

### Worked example: 9:40 am to 2:15 pm
- 9:40 am to 10:00 am: 20 minutes.
- 10:00 am to 2:00 pm: 4 hours.
- 2:00 pm to 2:15 pm: 15 minutes.

Total: 4 hours 35 minutes.

### Watch out: Time is not decimal
Do not subtract times like ordinary numbers. $2:15 - 9:40$ does not work, and 1 hour 30 minutes is 1.5 hours, not 1.3 hours.

## Reading a timetable

| Stop | Ferry 1 | Ferry 2 | Ferry 3 |
|---|---|---|---|
| Circular Quay | 08:10 | 09:25 | 10:40 |
| Milsons Point | 08:22 | 09:37 | 10:52 |
| Darling Harbour | 08:35 | 09:50 | 11:05 |

Read **down** a column to follow one ferry. Read **across** a row to see every ferry at one stop.

### Worked example: Catching the right ferry
Each ferry takes 25 minutes from Circular Quay to Darling Harbour (08:10 to 08:35).

To be at Darling Harbour by 10:00, catch Ferry 2, which leaves Circular Quay at 09:25 and gets there at 09:50.

## Reading a charges chart

Charts often charge one price to start, then a price for each extra part.

### Worked example: A phone call
A call costs 1.50 dollars for the first 3 minutes, then 0.40 dollars for each extra minute. An 8 minute call has 5 extra minutes:

$1.50 + 5 \times 0.40 = 1.50 + 2.00 = 3.50$ dollars.

## Time zones in Australia

The sun rises in the east first, so clocks in the east are ahead.

| Time zone | States and territories | When it is 12 noon in Sydney |
|---|---|---|
| Eastern | NSW, ACT, Victoria, Queensland, Tasmania | 12 noon |
| Central | South Australia, Northern Territory | 11:30 am |
| Western | Western Australia | 10 am |

### Key idea: Daylight saving
In summer, NSW, the ACT, Victoria, Tasmania and South Australia put their clocks **forward 1 hour**. Queensland, the Northern Territory and Western Australia do not.

So at 12 noon on a summer day in Sydney, it is 11 am in Brisbane, 11:30 am in Adelaide, 10:30 am in Darwin and 9 am in Perth.

### Challenge: Selective level: flights and slow clocks
A plane leaves Perth at 1:00 pm Perth time. The flight takes 4 hours 15 minutes. It lands at 5:15 pm Perth time. Sydney is 2 hours ahead in winter, so it lands at 7:15 pm Sydney time.

A clock loses 3 minutes every hour. It is set right at 8 am. By 6 pm, 10 hours later, it has lost $10 \times 3 = 30$ minutes, so it shows 5:30 pm.

A film is 2 hours 50 minutes long and ends at 9:05 pm. Count back 3 hours to 6:05 pm, then forward 10 minutes: it started at 6:15 pm.

**Mind map**

```text
Time
  12 and 24 hour
    pm: add 12
    Midnight is 00:00
  How long
    Jump to the hour
    Whole hours
    Minutes left
  Timetables
    Down: one trip
    Across: one stop
  Time zones
    Eastern, Central, Western
    East is ahead
    Daylight saving in summer
```

## Quick summary

- 24-hour time: add 12 to pm hours. 3:30 pm is 15:30, and midnight is 00:00.
- To find how long something takes, count up: to the hour, whole hours, then minutes.
- In a timetable, columns are trips and rows are stops.
- In standard time, Sydney is half an hour ahead of Adelaide and 2 hours ahead of Perth.
- In summer, daylight saving adds 1 hour in NSW, the ACT, Victoria, Tasmania and South Australia, but not in Queensland, the NT or WA.

## Quiz

Try these questions from the chapter quiz.

1. What is 2:45 pm in 24-hour time?
   - A. 02:45
   - B. 14:45
   - C. 12:45
   - D. 24:45
   - Answer: B. 14:45. Add 12 to the hour for pm: $2 + 12 = 14$.

2. What is 19:20 in 12-hour time?
   - A. 9:20 pm
   - B. 7:20 pm
   - C. 7:20 am
   - D. 9:20 am
   - Answer: B. 7:20 pm. $19 - 12 = 7$, and it is after noon, so 7:20 pm.

3. How long is it from 9:40 am to 11:05 am?
   - A. 1 hour 65 minutes
   - B. 1 hour 25 minutes
   - C. 2 hours 25 minutes
   - D. 1 hour 35 minutes
   - Answer: B. 1 hour 25 minutes. 20 minutes to 10:00, 1 hour to 11:00, then 5 minutes. That is 1 hour 25 minutes.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/selective-school-maths/time-and-timetables/#quiz