Time Duration
Learn to calculate elapsed time, convert between 12-hour and 24-hour time, and read timetables.
Calculating Elapsed Time
Elapsed time is the amount of time that passes between a start time and an end time. We can count on in hours and minutes to find the duration.
Elapsed Time = End Time − Start Time
Example: A movie starts at 2:15 pm and ends at 4:45 pm
Step 1: From 2:15 to 3:00 = 45 minutes
Step 2: From 3:00 to 4:45 = 1 hour 45 minutes
Total: 45 min + 1 hr 45 min = 2 hours 30 minutes
24-Hour Time
In 24-hour time, we count from 00:00 (midnight) to 23:59 (one minute before the next midnight). There is no am or pm — each time of day has its own unique number.
Conversion Chart
12-hour
12:00 am
24-hour
00:00
12-hour
9:30 am
24-hour
09:30
12-hour
12:00 pm
24-hour
12:00
12-hour
3:15 pm
24-hour
15:15
Tip: For pm times, add 12 to the hour. For example, 5:00 pm = 5 + 12 = 17:00. For am times, the hour stays the same (just add a leading zero if needed).
Reading Timetables
Timetables use time to organise events or schedules. You can use them to find start times, end times and how long activities last.
Train Timetable: Sydney to Wollongong
| Station | Train 1 | Train 2 | Train 3 |
|---|---|---|---|
| Sydney Central | 08:00 | 09:30 | 11:00 |
| Hurstville | 08:25 | 09:55 | 11:25 |
| Sutherland | 08:40 | 10:10 | 11:40 |
| Wollongong | 09:30 | 11:00 | 12:30 |
Question: How long does Train 1 take from Sydney Central to Wollongong?
Answer: 09:30 − 08:00 = 1 hour 30 minutes
Key Vocabulary
Elapsed Time
The amount of time that passes between a start time and an end time.
Duration
How long something lasts, measured in hours and minutes.
24-Hour Time
A time system counting from 00:00 to 23:59, without using am or pm.
Timetable
A chart or table showing when events or services are scheduled to happen.
Worked Examples
A swimming lesson starts at 10:45 am and lasts for 1 hour 20 minutes. What time does it finish?
Step 1: Add 1 hour: 10:45 + 1 hour = 11:45
Step 2: Add 20 minutes: 11:45 + 20 min = 12:05
Answer: The lesson finishes at 12:05 pm.
Convert 7:45 pm to 24-hour time.
Step 1: It is a pm time, so add 12 to the hour.
Step 2: 7 + 12 = 19
Answer: 7:45 pm = 19:45
School starts at 8:50 am and finishes at 3:15 pm. How long is the school day?
Step 1: From 8:50 to 9:00 = 10 minutes
Step 2: From 9:00 to 3:00 = 6 hours
Step 3: From 3:00 to 3:15 = 15 minutes
Answer: 10 min + 6 hr + 15 min = 6 hours 25 minutes
Knowledge Check
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Key Concepts Summary
- ●60 minutes = 1 hour. Always remember this when calculating time.
- ●Elapsed time = End time − Start time.
- ●To convert pm to 24-hour time, add 12 to the hour.
- ●To convert from 24-hour time (13:00 or higher), subtract 12 and add pm.
- ●Timetables help us plan journeys and find how long trips take.