what are the clocks?

Basically Mrs. Havisham received a letter at 8:40 on her wedding day that she was being abandoned by her husband to be. For her, life stopped at that moment. This is why the clocks are stopped there.

"It was when I stood before her, avoiding her eyes, that I took note of the surrounding objects in detail, and saw that her watch had stopped at twenty minutes to nine, and that a clock in the room had stopped at twenty minutes to nine."