I admit this is an extreme case but perhaps we should also examine the opposite scenario that is all too common. Let's say Harold is Gavin's colleague. Harold works the full 8 hours he is at the office, he believes strongly in "flow" so he doesn't interrupt his day with pointless activities like getting up to stretch or taking coffee breaks, he just brings a thermos to his desk and stays fully caffeinated that way. He finds it hard to "turn off" after work so he often spends time thinking about the next tasks he has to do and maybe puts in hours after work as well. At this point pretty much any developer can see where this is going, they know what Harold looks like, maybe they even were Harold at some point. Both Gavin and Harold are heading towards a blow up at some point. Neither of them are going to work out well for their employer in the end. I do think that Gavin is closer to the correct answer though, he's built in a lot of room in his estimates where if something does go sideways he has the ability to correct it and stay within the allotted time. If Harold mis-estimates something he will be working overtime or missing deadlines, perhaps both. Gavin should be working closer to 2/3 time than 1/3, depending on the overall accuracy of his and his boss's initial estimates of course.