Sprint length is determined during Sprint Planning, and should hold the time it will take to code the planned features in the upcoming Sprint, but does not include time for any testing.
It is best to have Sprints of consistent length throughout a development effort.
The length of the Sprint should be proportional to the work that is done in between Sprints.
All Sprints must be 1 month or less.
Sprint length is determined during Sprint Planning, and should be long enough to make sure the Development Team can deliver what is to be accomplished in the upcoming Sprint.