If you’re more concerned with how long a software engineer sits in front of a computer, opposed to the work they actually get done, you’ve already lost.

Edit: if you’re going to downvote me that’s fine, but please explain why “number of hours spent at computer” is at all a useful metric. It’s a genuine question; I’m not being facetious. I’ll get nothing done all day then wake up in the middle of the night with the solution to a problem. The amount of time I spend coding doesn’t really correlate with business value.