The opening hours are:
Monday – Friday: 8AM – 6PM
Wednesdays: 8AM – 7PM
Saturday: 9AM – 6PM
Sunday (& Bank Holidays) April – September : 10AM – 5PM
Sunday (& Bank Holidays) October – March : 10AM – 4PM
Monday 7th July: 2PM – 6PM
Where: Station Cycles, in the Grand Arcade in Com Exchange Street.
http://www.cl.cam.ac.uk/~dc552/GNUstepDevMeeting/
For the people that paid their one week bike rental with their accommodation, you can pick your bike there without paying anything.