How are the mirrors and clocks used as symbols in "Markheim"?

The store owner suggests that Markheim purchase a hand mirror as a Christmas gift for his lady-friend, and Markheim becomes furious.  He yells at the store owner that giving a woman a gift of a mirror was a "damned reminder of years, and sins and follies--[a] hand- conscience".  Looking in the mirror would only remind the woman that she was growing older and less beautiful with age.  The store owner jokes that his lady must be "pretty hard favored", in other words, unattractive, for Markheim to suggest that she would not like the mirror as a gift.  In this way, the mirror can symbolize vanity, as well as a reminder of the passing of time.

The clocks, too, symbolize the passing of time.  The constant ticking in the shop reminds Markheim that time is passing.  After the murder of the store clerk, the clocks in the shop as well as the nearby church clock strike three in the afternoon.  The loud noises disturb Markheim and remind him that he must continue with what he intended, which was to rob the store owner.  It is significant that it is Christmas Day, and the clocks strike at 3 PM because that is supposedly the time that Christ died on the cross, perhaps symbolizing the death of an innocent person (the shopkeeper).  Markheim, after being tested by his conscience, surrenders to his feelings of guilt and confesses to the murder.