An article focusing on Sky’s upcoming plans provides a tidbit of information which I believe narrows down when Game of Thrones is likely to premiere on Sky Atlantic (which begins to air tomorrow, February 1st, and will be free to all Sky customers through August). This paragraph seems to be a giveaway:
If that holds, and Sky doesn’t run any special “preview” airings of the premiere closer to the U.S. air date, I’ll go out on a limb and predict April 23rd as the launch of the series on Sky Atlantic. April 30th is the only other Saturday in April that’s available, but with almost two weeks between it and the U.S. premiere, it seems to us that Sky will recognize that for the error that it is. Of course, there are fans who’ll be hoping for an airing on the Monday following the U.S. airing, much as HBO Central Europe seems to be getting, and so this may be disappointing. Still, it’s only speculative right now, as Sky Atlantic has not confirmed an air date for the series as of yet.