Some of that time could just as easily be used up by them having to make trips to the bathroom or to do something else.
Any impulse or need could draw them away from where they were supposed to be and from what they were supposed to be doing.
If they had seen no change for so long and it was the same boring thing they had experienced for hours, then it would become even more difficult to focus on the task they had to carry out.
If they lacked the professional drive and willpower needed for that task, then it would be more likely that they would end up falling asleep, just as they could end up doing something else that could cause them to miss any activity on the screen.
It was already very late at night, so that person or those people would have spent many hours staring at the screen, seeing no change.
It only took a couple of seconds for the group to gain entry, and any of those possibilities could happen just as they took action.
