Timer Clock emoji is the picture of the device meant for informing someone when the certain period of time ends (by a sound signal usually) — i.e. it works just the opposite way the device represented by ⏱️ Stopwatch emoji does. The timers are integrated into many other devices where time matters like a microwave. And the emoji is used in every context related to time.
Examples of using
“The cake will be ready in 20 minutes ⏲️”
“I need to work out for an hour ⏲️”