can any one tell me the name of the movie?

It was released either end of the 70's or early 80's it starts with a boy sat in his room bored when a giant box tied with ribbon floats through the window. he opens it and steps inside. At this point the film turns to animation. inside the box he explores a world. three main point i remember are a dog with a watch in his chest (he's a watch dog). At one point in the film he gets stuck in the duldrums ( a swamp like area with creatures that look like oozing mud). Finally a tall thin creature with no face that wants him to move a mountain of sand from one location to another, one grain at a a time using tweezers.

Other details which i'm sketchy about is there is a guy called the whether man not weather man.

the fates make an appearance.

finally he emerges from the box which closes and back to live action. The box then floats off out of the window.