Multiple measurement firms put 18 to 24 year old daily phone time near eight hours, with social and short-form video accounting for the largest share. That number is not the problem on its own. The problem is the shape of the cost. A working adult who scrolls for three hours at night loses sleep. A student who scrolls for three hours at night loses the thing the next twelve months of their education was supposed to produce.
Most screen-time apps were designed for the working adult. Their default tone is "find balance" or "be more mindful". That tone fails students for the same reason willpower fails students: an undergraduate brain is still finishing prefrontal development, and an undergraduate calendar has more unstructured time than any other phase of adult life. Soft reminders, ignorable banners, and dim-screen prompts collapse against that combination.
ScreenFine assumes the willpower path has already failed. Set the limit when you are calm, in week one. When you cross it during exam week at 1am, the apps lock until you complete the redemption you picked in advance. The deal was signed when the rational version of you was in charge.