I have found that CodeChef actually plans their contest much ahead of time. For example
- The December Challenge 2016 has been set from Friday, 2nd December, 2016 15:00 to Saturday, 12th December, 2016 15:00 (IST)
- The December Cook-Off 2016 has been set from Sunday, 18th December, 2016 at 21:30 to Monday, 19th December, 2016 at 00:00 (IST)
- The December Lunchtime 2016 has been set on Friday, 25th December, 2016 from 11:00 A.M. to 2:00 P.M. (IST)