The concept of releasing in different parts of the world at different times is outdated. Release worldwide all at once.
But it's not that simple. HBO isn't a worldwide network. They need to make deals with lots of different networks in different countries and that takes time. Those networks then need to fit the show into their schedules.
National networks are similarly outdated. This is the 21st Century, for crying out loud.
If a bunch of kids can propagate high quality 1080i/720p copies of television broadcasts around the world literally within half an hour of the show airing in its native market, the content owners themselves can manage the same.