Surprisingly, this is not a Hitchhiker’s Guide to the Galaxy reference, but an actual fact. From Burnout: Solve Your Stress Cycle, by Emily and Amelia Nagoski
Edit: Here is the full text from the image and the end of the sentence that’s missing:
[Forty-Two Percent
So how much rest is “adequate”?
Science says: 42 percent.
That’s the percentage of time your body and brain need you to spend resting. It’s about ten hours out of every twenty-four. It doesn’t have to be every day; it can average out over a week or a month or more. But yeah. That much.
“That’s ridiculous! I don’t have that kind of time!” you might protest - and we remind you that we predicted you might feel that way, back at the start of the chapter.
We’re not saying you should take 42 percent of your time to rest; we’re saying if you don’t take the 42 percent, the 42 percent will take you. It will grab you by the face, shove you to the ground, put its foot on your chest, and declare itself the victor.]
Note: This refers to rest in general, not specifically to sleep. These are average figures; individual circumstances will vary.
[yelling out towards an empty dashboard] HELLO??????????????????? DEAR GOD HELLO????????????????? [my mutuals are asleep and wont be up for a while] ANYBODY????????????????????????????????????