It's banal to say "this was 2013" as if such results age so quickly.

It amazes me how on one hand "Peopleware" (1987) and "The mythical man-month" (1975) are held up as ground-breaking ideals here but a published academic study is dismissed because "it was published in 2013".

As for "Well it's not transferable to 12 hours a day with no holidays", what you're describing isn't reality for most people in most countries. It is not even legal to work 12 hours a day for 5 days a week in any of Europe+.

If you are doing 12 hour days and don't have holidays then you are a slave not a worker.

+ Except UK, but only if you have specifically opted out of the law, otherwise the 48 hour week maximum still applies.