People will be familiar with the exhortation to "begin it now". That's good general advice of course. But I think it's also particularly pertinent to any project on the internet. The reason is that the age of a domain is a factor in SEO. You accrue a small amount of benefit simply for hanging around in cyberspace for a while.
That's why if you have an idea for a website, you should choose a good domain name ASAP. Put some related content up there, even if it's far from perfect and it doesn't look too flash. Then get at least one link back to it so that it gets indexed by Google.
You will have started the ball rolling then, in more ways than one.