Stronger was released Jan 17th US and Feb 3rd UK. That's 17 days apart, or 2 - 3 weeks
So the U.S should expect it between the 10th-17th May can't wait!
(although i'm super pissed about it being so late in the UK, it's REALLY going to damage it seeing as Stronger is practically gone now...)
EDIT: after posting that just occured to me..
Stronger - Feb 3rd UK
Dark Side - June 3rd UK
Stronger - Jan 17th US
Dark Side - May 17th?