The words “half-life” are important and if you search for NyQuil advice you’re going to get chat bot output which doesn’t understand how this works, because it needs math.

10-12 hours half life doesn’t mean it’s ineffective then. It means it’s still 50%. So that 6-pints-drunk becomes 3-pints. 10-12 hours again (a full day), 1.5 pints. Another 10-12 hours, 0.75 pints. So exactly lining up with my experience.