[whpalmer4]

A 1 hour long meeting of 2 people has a duration of 1 hour, and an effort of 2 hours. If a third person attends, the duration remains 1 hour, but the effort goes up to 3 hours. Perhaps the most memorable statement of this idea is "9 women can't make a baby in 1 month" :-)

A task which takes an hour of effort by the assigned resource, but can be done any time prior to a week from today, has an effort of 1 hour and a duration of 1 hour, and an end constraint set to the date/time by which it must be completed. The constraint will force OmniPlan to put that hour in the schedule before the deadline, or show a violation if that is not possible.