A target person is chosen then the researcher watches them for a fixed amount of time, and records their behaviour during that time. After this time they wait a fixed interval and then either watch them again, or watch a new target person.
So, time sampling involves observing one person for a set length of time at set intervals.
E.g.: The researcher observes one child for 1 minute, waits 30 seconds, then observes them again for 1 minute.