The scores on the application are "self reported", meaning that you tell them what you scored. So if you can say on January 6th what your composite score is, you're all set. They verify the score later in the admission process. Usually they don't check the offical report until you're fairly far along. The idea being, why waste time verifying with GMAC, if they decide to pass on you.
Some people would ask, why wouldn't you just put in a high score then? Well think it through. Let's say you put down a 710, and you make it all the way to the interview. They decide they want to accept you and then, as part of protocol, they verify all the scores and grades that you put down in your application. They find out you really scored a 690. Oh, oh. Now you are screwed. They will view you as dishonest, or wasting their time, or if nothing else, unable to work a computer keyboard. Either way you're application is done and you won't be admitted.
There are two problems with taking the test the day before the application is due. One, can you really focus on preparinig for the GMAT while writting your essays and encouraging your references? And , two, you will not have your AWA scores back, so you'll have to put down To Be Determined, which may negate your application, or at least put you in the check back later pile. Not a good thing. That's why MBA.com says 3 weeks. It allows them time to report your AWA scores.
Hope that helps.
