How is the party always getting disrupted?

The party at Prince Prospero's secured abbey is consistently being interrupted, each hour, by the chiming of the ebony clock that can be found in the black and red room, the seventh and last of Prospero's many colored rooms.  When it strikes, on the hour every hour, "for a moment, all is still, and all is silent save the voice of the clock.  The dreams are stiff-frozen as they stand."  When the masquerade guests hear the clock chime the hour, they all stop dancing, stop moving entirely in fact, and listen in silence.  Then, as the sound of the chimes die, the party-goers slowly begin to move and dance again.  
The guests actually stay out of the room in which the clock stands; perhaps it reminds them of mortality in general and their own, in particular.  The room is hung with the colors of black and red, often symbolic of death and blood, respectively, and it contains a clock, another symbol of mortality, as it keeps track of time.  The masqueraders have escaped to the abbey to forget about the terrible disease decimating the kingdom, and this room can only remind them of it.  Therefore, when they hear the clock at midnight, there is "an uneasy cessation of all things as before"; however, the stillness and anxiety is even more pronounced because the clock takes so long to chime twelve times.