Our organisation has always used two week iterations and sometimes we do wonder if two weeks is optimum, Well the first thought was for enhancement projects two weeks fits the bill, these could be projects where the solution to implement the features is available to the team, but for a brand new project which includes a technical learning curve and innovation, three weeks might be be apt. This is subject to discussion with the teams. Although Scum recommends a 30 day iteration, 2 week iterations yield results and 3 week iterations will yield innovative results. At the end of the day both iteration lengths are within the realm of Scrum and it is a variable available to teams and the product owner, how it is varied or used as long as the goals of the release are met, is not important.
Based on previous experience with two week iterations I have made some observations which kind of remind us the strength of the two week iteration
- Two weeks is just about enough time to get some amount of meaningful development done.
- Two week iterations indicate and provide more opportunities to succeed or fail.e.g, within a 90 day release plan, 5 - 2-week iterations of development and 1 stabilisation iteration at the end make it possible to have checkpoints on the way to the release.
- The 2-week rhythm is a natural calendar cycle that is easy for all participants to remember and lines up well with typical 1 or 2 week vacation plans, simplifying capacity estimates for the team.
- Velocity can be measured and scope can be adjusted more quickly.
- The overhead in planning and closing an iteration is proportioned to the amount of work that can be accomplished in a two week sprint.
- A two week iteration allows the team to break down work into small chunks where the define/build/test cycle is concurrent. With longer iterations, there is a tendency for teams to build a more waterfall-like process.
- Margin of error for capacity planned and available is lesser in two week iterations.
Well the above is on the basis of what I have observed and may be different in your organisation.