Do it yesterday. Send it registered mail. Until the copyright office receives it, YOU DO NOT HAVE DMCA SAFE HARBOR PROTECTION! It's not the only thing you have to do, but an important one.

See Viacom v. YouTube:

http://en.wikipedia.org/wiki/Viacom_International_Inc._v._Yo....

http://arstechnica.com/tech-policy/2012/04/second-circuit-ru...