A time horizon (or deadline in the context of task? management)) is a fixed period in time, or one that changes only regularly, e.g. every 10 years?, every 4 years?, every 3 years?, every 2 years?, every year?, quarterly?, monthly?, weekly?, daily? or less often.. After the horizon has passed, none of the logic or argument that applied before it is valid.

For instance, if one commits to something given an urgent deadline (say end of year? or end of month? ) then any such commitments lapse if the deadline is not met.

See wiki meeting, TIPA and backcast to fixed time horizon for the most important implications.