I've set myself the 100km challenge. At the very minimum I have to ride one metric century (100 km, 62.18 miles) in every month to succesfully complete the full challenge. Only single continuous rides of at least 100km qualify, not a daily or weekly total of several shorter rides that exceed 100km. Tea stops are allowed.
My target is to comfortably exceed the minimum of one century ride per month, starting November and finishing October 2013.
So far I've completed two over the last weekends.