The Time Box
So what is a time box? Put simply it's an agreed fixed length of time that a team or individual will use to accomplish a goal. At the end of the period of time the team stops - regardless of if the task is complete or not.
Within Scrum, time-boxing is used to set the length of a sprint (iteration), 2 Weeks is common but I've worked with 1 week, and 4 week sprints and I know of a few Scrum Masters who have experimented with 1 day sprints!
Ceremonies should also be time-boxed - Probably the most famous of which being the daily stand-up - 15 minutes is a common allocated time but it depends upon the team and importantly the size of the team.
In addition to the stand-up every sprint should also consist of a planning session, The review (AKA the demo) and the retrospective. The lengths of these should be decided within your scrum team but as a quick rule of thumb - if doing a 2 week sprint a 4 hour planning session should be sufficient and an hour allocated to the review and the retrospective.
Time boxing as a philosophy is one of the fundamental key differences between Scrum and Waterfall - Where as in waterfall the time is extend until the full scope is delivered - within Scrum the time scales are fixed but the delivery/scope is variable.
Put simply time boxing is a way to maximise delivery by focusing on what's important.
Thanks for reading,
For those who are interested - I believe 3 to 8 minutes are common time-box lengths for speed dating events!