This is the part that feels wrong: you got more time and you're choosing not to use it. but that's the whole point.
a study from 1999 by Brannon, Hershberger and Brock ran this experiment three separate times. they gave students extra time on a task and watched what happened. the students didn't do better work. they took longer to do the same work. Another study by bryan and locke from 1967 found the exact same thing give a group double the time they need, they use all of it, with no improvement over the group given the minimum.
The name for this is Parkinson's law. Work expands to fill the time you give it. I if you already had a prep plan that was going to get you ready, more hours on the same subject mostly produce slower hours, not better ones. the freed days are worth way more redirected somewhere you were rushing.
If you hadn't actually started the material yet and the original plan was a panic plan, the extra days are real. this rule is about review time, not about catching up on stuff you never learned.