What functions should we write for the design deadline?
None whatsoever. All you need to turn in for the design deadline is your set of data definitions and the animation examples captured in your definitions. For example, we were able to write examples of slideshow talks before we wrote the interpreter. Something akin to a sample talk program is what we're expecting with your design.
Do the Polygons need to be filled in?
No.
Does the programmer specify the canvas size, or is it hardcoded?
Either is fine (your choice). 300 x 300 is a good canvas size.
Can we use set!
You may use set! to store the time at which an animation started. You should not need it for anything else.