My policy on billing is, "Would I be doing this if I wasn't on this project?" If no, I bill, if yes, I don't. So, would I be sitting in a client's office, potentially (usually) (relatively) far away from my home, dressed in nice clothes, unavailable to other clients for that time, if the client hadn't put me on the project, even if I drift on to Hacker News for a few minutes? All office hours are billable.
That said, since I spend such a small proportion of my time in a client's office, I do try to stay focused. I typically don't look at Hacker News or anything like that. I got sick of setting everything to use SOCKS proxy so I set up a VPN, but I didn't bill the client for this (30 min or so) despite my normal policy. My real billing policy is "bill fairly".
I think he's attempting to explain that he hasn't actually done anything (maybe loading up some programs, getting reference material together, etc.) and then does something unrelated. I wouldn't bill for that either unless it took a significant portion of time AND I wouldn't have to do it again later.
And of course there's no real mechanism to not get paid for time spent daydreaming if you're sitting in an office on salary.
On the point in question though, no, I won't bill time warming up the dev environment unless I actually use it for productive work. You lose the odd fraction of an hour here and there, but really if you're trying to add up things like that to get yourself paid an extra 2 hours at the end of the week you're probably just not charging enough for your time.
Why? I bill for work done regardless of my location, I never thought it might be out of the ordinary.