The author used situational irony in the passage. It was ironic that Jeremy wasted all his time studying for a time management test, only to have the text actually be the next week.
Situational irony is a literary device that you can identify in a piece of writing when the outcome of a story, or statement, is opposite to what you, the reader, expected. This outcome tends to be whether tragic or humorous. When reading the first sentence of the excerpt, the reader may expect that Jeremy is good with time management, as he spent all weekend studying for it. However, the outcome turns out to be the opposite of that, and becomes humorous at the same time, as Jeremy had mistaken the day of the test!
