Not sure which part you're referring to, that doesn't work.

Average 10% spend by an engineer towards hiring is quite normal, from my experience. Obviously, it's average, so there are some who spend way more than 10%, and there are some who don't spend any. 4 out of 40 hours a week including phone-screens, on-sites and deliberations is easy to get to.

I'm sure you know, that a lot of hiring at that scale is systematized and (hence) heavy-lifting is done by non-technical recruiting people.