Hi Katie, welcome to the boards. Congratulations on your upcoming graduation!
In high school, sometimes the best time to exercise is right after school. You give your brain a break, work off any residual stress from the day, and get energized for studying in the evening.
College is going to be very different from 8 - 3 every day grade school. Your schedule will probably change semester to semester and classes will be at different times each day of the week. Right now through the summer it might be easier to keep a regular schedule, but my tip is at the beginning of each semester, check your class schedule, decide how many hours per week you need to study, block out time in your calendar for class / study time (google calendar makes this really easy), then see where your holes are and fit exercise into those holes.
You can even block exercise time into your calendar. Subconsciously it's like making an appointment with yourself for exercise, so it's easier to stick to it.
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).