Do we count work as "being in the office/lab"? Or do we count work as thinking about the problem?
If one were building a company like Tesla for example, I would count going to the gym and thinking of the problem domain while running on a treadmill as work. I would also count thinking of the problem while going for a walk as work.
If one has really set one's teeth into a nasty problem, things like going to a party, or social calls like seeing friends not engaged in the problem, isn't relaxing, it's frustrating.
I think we should redefine the parameters of this conversation into time that depletes the body and time that replenishes it.
Being in front of a computer for long periods is hard on the eyes, it can be hard physically especially if the ergonomics aren't perfect. Being at the office for long periods can be draining as well because unlike being at home there aren't places to go that are replenishing on demand.
If one has a good sit/stand desk and spends a lot of time coding while standing, 10 minutes lying on a bed is incredibly replenishing for example.
The other dimension here is that perhaps it is alienated work that is inherently depleting. Working for someone else, or on something one does not really want to be working on is draining.
Working on something you care about is invigorating and I can't see how spending less time in that state can possibly be more productive than more time in a productive, non-depleting state.