Never mind 300+ hours, I've seen people claiming 1,000+ hours which would have required 16 hour days, EVERY day, since release day. I've not wanted to call these people liars, but Jesus I can't even begin to get my head round how that's possible without insanity at the very least.
Having absolutely nothing else to do would definitely help...
I'd get a huge headache from something like that, but i'm sure a few people are capable of managing that... You just need to be unemployed/retired or something.