No, of course you have to take into account known factors, like sometimes it rains. And if it is difficult to add a new type of release schedule, it is not poor

No, of course you have to take into account known factors, like sometimes it rains. And if it is difficult to add a new type of release schedule, it is not poor planning, it is a poorly designed system. When we don't know how requirements are going to change, we must not guess, we should instead design the systems so they are easy to change.