LOL SDN math. How about time spent doing things like showering, cooking food, occasional conversations with friends or roommates? Errands? I spend the least time on my social life out of all my room mates and the premeds I know well, yet I still find it difficult to spend 20 hours a week on ECs, the most I go for is about 15 hours a week as I don't do research yet, but I find it just exhausting to be constantly doing these things that require a lot of attention.
But yes there are a few people I have even met personally that are very smart and study less than most others and have better social lives than people like me and double the time I spend on my ECs.
This is also very underestimated, I didn't think it was so apparent until I saw it with my own eyes. People generally take it during midterms / finals week, but I have met a few people who almost live off of it.