I started playing Magic (or started again rather) just after the Theros set had come out. The standard format was defined to include the Return to Ravnica block and the entire Theros block of which the last two sets had not come out.

I do not think Wizards of the Coast has made any official announcements yet so I'm asking for what may happen based on what has happened in the past. When can I expect Standard to change and what should I expect? Is it likely that the Theros block will remain in and the Return to Ravnica block will drop, or are the changes unpredictable?