“studies show that “deep sleep,” which is concentrated in the first half of the night, is most valuable for retaining hard facts—names, dates, formulas, concepts. If you’re preparing for a test that’s heavy on retention (foreign vocabulary, names and dates, chemical structures), it’s better to hit the sack at your usual time, get that full dose of deep sleep, and roll out of bed early for a quick review.”
―
Benedict Carey,
How We Learn: The Surprising Truth About When, Where, and Why It Happens