Final answer:
In the opening of Act IV, daybreak signifies the scheduled execution of a prisoner, marking the end of one's fate.
Step-by-step explanation:
As Act IV opens, the event that is set to take place at daybreak is the execution of a prisoner. This moment is marked by the rising of the morning sun, which brings the end of night and the beginning of a new day, often symbolizing the inevitable approach of fate and the finality of the prisoner's destiny. The advent of daybreak in literature marks a transition, sometimes depicting hope and new beginnings, but in this context, it signifies the solemnity of an impending execution.