I use this 20 minute activity to practise the 12 and 24 hour clock with my students.

Each student has a mini-whiteboard. The task is clearly differentiated into:
All: Draw the time in analogue and/or digital.
Most: Unjumble the Extra time.
Some: Change both times into the 24 hour clock

I give them 30 seconds to attempt to do as much as possible.
Click the PowerPoint to reveal the unjumbled and 24 hours clock answers below.