A movie about a dog who loves time, a math wizard, and a boy who lives in london.?

i forgot this movie. i remember watching it in the 90s. I remember a boy riding a bike into the big box which leads him into the new world. some of the scenes are when a dog explains about how time is precious and is never wasted. and another scene with a math wizard that asked for the biggest number imaginable, but by adding 1, numbers go on forever. i really hope someone knows what i'm talking about with this vague description of this movie.