Summertime Saga is segregated into days which contain three time
slots - morning, daytime, and evening. All of these time periods will
allow you to do different things and most goals need to be completed
within a time limit so sleeping unnecessarily can skip your whole day
and waste a bunch of time.
Even in the evening when it can be hard to find something to do you can participate in rap battles or play on your computer to help raise your stats.