Ok, so I did some more testing last night and checked the timer this morning. I made a mark on the defrost timer last night to see if it had advanced, and after checking this morning it had moved quite a bit. I took some measurements in voltage at pins on the timer, and came up with test values (all referenced to ground):
Pin 1: 120V
Pin 2: 0V out of defrost mode; when in defrost it is 120V
Pin 3: 120V
Pin 4: 120V
All are as to be expected. However, I checked the timer for advancement a few moments ago, and it has not seemed to have moved since checking it this morning. I checked the above pins again, and came up with the same results. So, the timer only advances when the defrost thermostat is closed from my understanding. However, when I check for a drop across pins 2 and 3, I get a value of 120V, which would indicate that the defrost thermostat is closed, correct? If so, then is there any reason why the defrost timer has stopped advancing? The compressor has been running, so it should definitely be moving.