There is an old expression, "Oh, what a difference a day makes!" and in the narrative of Schatz, the day that he spends waiting to die--he believes--changes him irrevocably. Left alone by his father, who does not realize that the boy has a misconception of the gravity of his temperature thinking it has been measured in Celsius rather than Farenheit degrees, Schatz spends a day absorbed in existential struggle that greatly burdens one of his young age.
Hemingway's is a "local color story" that revolves around a slice of life and its philosophical implications. The "day's wait" of Schatz is life-changing as after his lonely battle with fear, there is a backlash to this day's traumatic experience and he loses his stoic courage:
But his gaze at the foot of the bed relaxed slowly. The hold over himself relaxed too, finally, and the next day it was very slack and he cried very easily at little things that were of no importance.
Surely, this one day has had a lasting effect upon the psyche of the young boy, making him more detached and less innocent than he should be for one so young.
The action in Ernest Hemingway's short story, "A Day's Wait," takes place over the course of one day. In the opening of the story, Schatz (the son) has been running a fever. His father, who remains unnamed, calls for a doctor. The doctor diagnoses Schatz with the flu and tells him that a temperature of 102 degrees should not be any concern, until it reaches 104 degrees.
Schatz's father maintains a bedside vigil until Schatz's preoccupation with his illness overcomes him. Schatz's father decides to go out to take the dog for a walk and hunt, while Schatz sleeps. Upon returning, Schatz's father takes his temperature (which has not changed). Schatz asks his father about his temperature and his father lies telling him it is only around 100 degrees.
After a conversation about the differences between the measurements of Fahrenheit and Celsius, Schatz's worry seems to change.
The next day it was very slack and he cried very
easily at little things that were of no importance.
Therefore, the title of the story is justifiable given the way Schatz's feelings seem to change after a day has gone by.