It depends. Most terminate after 10 to 11 minutes max, regardless of coil conditions, but usually there is another way to terminate as well.
Most (Time/Temperature Defrost) also have a coil thermostat that terminates after the coil warms up to between 60 and 75 degrees.
Some (with demand defrost) have a coil thermistor that electronically senses the coil and outdoor air, then terminates after the coil warms a certain amount above the outdoor air temperature.
Trane & York use mostly demand defrost.
Lennox and Carrier use some time/temperature & some demand.
Most other brands that I am familiar with use time/temperature terminate.