Your website will be copyrighted as soon as you create it -- creating the HTML file is "fixing in a tangible form", and is all that is required for a copyright.
You won't be able to sue someone for copyright infringement until you register with the copyright office, but you actually own a copyright as soon as you fix an original creative work in a "tangible format" -- writing it down on paper, writing the HTML code, etc.
The "poor man's copyright" doesn't give any more or less legal rights to the creator -- the work is copyrighted as soon as it is fixed, and you can't sue until you register with the copyright office. I suppose the "poor man's copyright" could be used as evidence to show a date of creation, but it doesn't give one any more rights than if they hadn't used a "poor man's copyright".
I am not an attorney, and this isn't even remotely legal advice.
