Cutts recommends taking down a parking page about a month before launching a new site.
Google web spam czar Matt Cutts just published a video in which he asks himself a question (rather than taking it from the community): should I keep a domain name parked before I launch a web site?
In short, Cutts says no.
He works in a reference to eNom’s backpack girl and then goes on to explain that Google has a filter to try to keep parked domain names out of its search results.
This filter doesn’t immediately know when a domain changes from a parked page to a “real” web site, so he recommends putting up a placeholder page 3-4 weeks before launching a site.
That placeholder page can be something as simple as “coming soon” with a few lines of text — just make sure it’s not an ad-filled parking page.
Here’s the video: