There is no restriction on weekend work in the Sprint extension. The "Ideal Points" line assumes that it is not ideal for people to work 7 days a week, and thus it includes a two day "flat line" where tasks are not expected to be completed. However, this does not preclude the fact that a task can be worked on during the weekend and closed on Monday morning.

@Christopher I don't understand the assumption, particularly for open source software projects where people often work (and close tasks) on the weekend. In my opinion, and from numerous others that I've heard feedback from, this is really confusing.

@Christopher I agree that working on weekends is not a sustainable style of work, but I do think that it's up to the teams to decide when they work.

From my extensive experience in project management scheduling and the use of Gannt Charts to estimate completion, allowing lag, float or "slack time" is important in maintaining a realistic projection. The flat line is not really anything but a float allowance. It defines a time period where the expectation of task completion is absent. The alternative of defining a projection without a float is an aggressive estimating method, and even for open source projects, not really practical. Where the slack occurs naturally for most teams is on the weekend, but this is an arbitrary assignment and does not really matter. The bottom line is that for every 7 day work period, at least 2 days of process slack should be allowed for an ideal projection.