Each day begins at 6:00 AM, and you are free to spend it as you please. Whether you want to hang out with other characters, train to improve your stats, or prepare for a battle against the Kegai, you should set a goal for the day and see it through.
Study, Study, Study
Head to the high school from Monday to Friday between 8:00 and 9:00 AM and enter Classroom 1-A on the second floor to take supplemental classes, which will boost Nini's Intelligence and Social Status. While you can still join the class if you're late, you'll receive reduced benefits.