Symbolism, Imagery, Allegory
Clocks make an appearance twice in the play. In the first act, the clock strikes noon, and Olga is transported back in time: the clock struck the same way on the day their father died. As far as we know, clocks usually always strike the same way at noon, but that's not the point. The prominence of the clock indicates how the passing of time is a major theme in the play.
Don't believe us? When Chebutykin smashes an heirloom clock (possibly the same one as in Act I; Chekhov doesn't specify), he's railing against time, life's unfairness, his own suffering, and the suffering of the women he loves. If smashing a clock isn't a symbol of responses to time passing, we don't know what is.