On September 10th, the CFTC staff issued a "Q&A" responding to questions from market participants on the timing of when entities will be required to register as swap dealers.
The "back of the envelope" answer is no earlier than December 31, 2012, if a particular entity's swap dealing exceeded the de minimis threshold during the period from October 12th (the effective date of the CFTC's swap dealer rules) and October 31st of this year. After than, an entity will be required to register no later than two months after the end of the month in which that person becomes no longer able to take advantage of the de minimis exception under the swap dealer rules. Although, the CFTC did clarify that nothing prevents an entity from registering as a swap dealer at anytime after the effectiveness of the swap dealer rules.
The Q&A is available here.