I take your point that you could argue that the ten days would produce disutility or at least very little utility, however the point is to answer the question in the least possible world - where the ten days actually are about as good as regular days. If you're having trouble imagining that, make it twenty or thirty days, or whatever you think would be equivalent to ten regular days.

To say nothing of the monetary expenses and moral problems that would result from committing murder.

Well, the whole point is that the revealed preferences from Kawoomba's post above should easily overrule such considerations, and therefore checking whether they do or not should clarify whether he's acting under extreme scope insensitivity or some other confounding factor.