Ummm, I'm no expert - but as far as I recall that's something you should be able to do almost immediately... Sorry for feeding you misinformation if I'm wrong!
you can add anything to your signature right away! just make sure you read the signature regulations (it's on a sticky somewhere on the boards..sorry I don't have the link handy!) But it's not hard to find.
Everyone goes to tickerfactory.com for their calander countdown...have fun!