Quoted directly from the Nevada State Athletic Commission website.
A timekeeper additionally assists the referee in counting for knockdowns to assure the fighter has the correct amount of time to return to the contest.
A timekeeper usually works in tandem with a partner so that there is consistent observation of the contest. One partner is responsible for reading the various clocks and the other observes the contest and verbally calls out time intervals to his or her partner. Working together, the timekeeper provides the officials with all information related to timekeeping and must be able to react to unique and unexpected events that take place during a contest.