The competition runs until February 5, 2017 and is open to all almost all Radeon fans worldwide (except a couple of countries that are restricted from business in the US, which includes countries like Cuba, North Korea, Sudan, Syria and Myanmar).
AMD will select two winners and promises to distribute the prizes to the winners upon completon of the sweepstakes. The terms & conditions state you should allow up to 28 weeks for delivery of any prize, so it doesn't really provide a clue about the potential Vega launch date.