Anecdotal evidence, I used to to that as a CSR at PayPal years ago. After a "normal" day of height hours of calls or emails you had two more hours of emails.

My brain was fried and I was glad when the policy was canceled.

I loved the extra day though (which was Monday or Wednesday) and as a software engineer I would love to pull it off, to rest or work on my own thing, but I would gladly take a pay cut than work 10 hours a day constantly.