Redsy:
Don't see why not you can do what you said. The "timer" will control the recept and the post light. There is no requirement (resi) that I am aware of that a "switch" has to be in-line. I would make sure the recept is GFI with a "bubble cover ('02 NEC, since you have to touch it. Make sure the CB is marked, afavorite of some inspectors.
John