Before replacing your timer with a new one, you may try to lubricate it first to see if it fixes the issue.

Apply WD-40 to the timer's slight peek edge.

Let the WD-40 sit and take effect for around 30 seconds or a minute after you spray it onto the timer.

The WD-40's oil will seep inside the timer, reaching the tiny gear of the timer.

WD-40 is flammable. Be sure to read the instruction label before using WD-40 Two-Way Spray Can.

Not cleaning/wiping off excess WD-40 oil on the timer will start a fire in the toaster oven.

You can test the timer using a flat head screwdriver to turn the timer to see if it ticks/works.