I broke this rule and didn’t get my video up until 7 days into my project.  I am not sure if it really made a big difference for this particular project.  If you don’t have a video you need to have really nice images on the project page that explain the project and help you tell the story.  I learned that video is really tough to do right, but with a little research you can put something passable together.  Mine was terrible, but maybe that helped this particular project.  A great video can really help a good project become a runaway hit so it is definitely worth making, but beware that a cinematographic masterpiece will take a lot of time and effort.