I just read in the What's New section, linked from CS50's main course page on edX, that Hackathons and office hours will be held in various cities outside the United States during a certain time frame. Where exactly in those cities will these events be held? Will it be mentioned later in the course page?
Once the details for the office hours and hackathons are worked out (they are still in the planning stages), you'll find more information on these pages:
Office Hours: http://cdn.cs50.net/2015/x/events/hours/hours.html
Both of those are linked from the sidebar on the Courseware Info page.