The title "A Day's Wait" refers to the time period in which a young boy learns the significant difference between Centigrade and Fahrenheit.
In the story, Schatz is afflicted with a bad case of influenza. He learns that his temperature is a hundred and two degrees. The doctor fails to mention, however, that this measurement of his temperature is in Fahrenheit. Unbeknownst to the doctor, the boy believes he is going to die; he does not realize that body temperatures can be measured in either Centigrade or Fahrenheit.
Fearing that his life is at an end, Schatz wills himself to remain stoic. He reigns in his emotions and tries to face death with courage. Schatz even forbids others from entering his room; he does not want anyone to catch what he has. Meanwhile, his white face testifies to his intense emotional struggle. It is only after his father apprises him of the truth that Schatz begins to relax. So, the title refers to the time period in which a young boy learns the importance of verified knowledge. Schatz comes to understand that there is a significant difference between Centigrade and Fahrenheit.