This study aimed to determine the effect of time of day on learning Mathematics by examining the optimal time of day to teach mathematics in a high school setting. Using a quantitative study, the data was gathered from high school students in Karachi-based schools. Classroom polls were used to obtain data for this research study. The sample included high school students, currently enrolled in VII grade (sections E and F). The school was associated with the Aga Khan Board. The findings of the study revealed a statistically significant relationship between time-of-day and the learning achievements of students and students’ performance in mathematics. As students learn more efficiently when they are taught and graded during their preferred time of day; therefore, it is recommended that parents and school management should pay attention on the students’ preferred learning timing.