clock
beat the clock: seebeat.
clean someone's clock: seeclean.
round (or around) the clock all day and all night; ceaselessly.
1992Susan SontagThe Volcano Lover The mountain was…guarded round the clock by a ring of armed soldiers mounted on nervous horses.
turn back the clock return to the past or to a previous way of doing things.
watch the clock wait eagerly for the end of working hours.
☞ It is from this expression that the word clock-watcher has developed, referring to someone who is determined not to work more than their allotted hours.