12-hour days are less horrible in the week immediately following a move. The apartment is going to be a mess no matter what, so it doesn't really matter that I'm stumbling back in the wee hours and just collapsing into bed. Also, unlike the pre-move packing madness, unpacking can sort of proceed (or, in this case, not proceed) at its own pace.
That said, these 12-hour days are objectionable for other reasons.