My wife's working in a major European corporation and they do one/two weeks shifts. They also have it divided into classes of problems they're fighting (the "need it solved now" vs "this weird thing happened and we think it's your team's fault" vs "OMG it's 3 am and the world is on fire!"). I can't recall now which class corresponds to which duration.

Edit: there's also one person who is the permanent point of contact for a single release. New releases are once per three months. This person obviously has one hot week, but the amount of contacts decays exponentially.