With digital clocks, kids don't always understand the passage of time. They're just numbers on a screen, after all. Using an analogue clock with some Post-it notes helps them visualise when a deadline is approaching.
Parent Hacks explains how this tip helps kids manage themselves:
Not only does this help her see the relationship between different tasks and the passage of time, it gets her in the habit of checking the clock, not waiting for the timer (or me) to prompt her to move along. The goal is to eventually wean her off the timer as she learns to manage her own time.
Most analogue clocks don't need power from a wall outlet, so you can put the clocks anywhere in the house. Check your local discount store for some inexpensive clocks with "big hands" and "little hands."
Post-it Notes analogue clock = time management tool for kids [Parent Hacks]