I'm not sure where you are located, or what the average guest situation is, but where I am is more of a throughway and I usually ask guests how much driving they have ahead of them. Cell phone service is spotty from here to anywhere, making the liklihood of someone writing the review on the way really unlikely. I agree about a week is enough time for most guests to get back home/in their regular routine, and then be receptive to sitting down and writing that review.
You can even frame it in a caring way, i.e. "I hope you have arrived home safely, thank you again for your stay. I completed your reivew and said this "blah blah". If you have a moment would you consider reviewing your stay?"