Duration, n.
Etymology: [OF. duration. See Dure.]
The state or quality of lasting; continuance in time; the portion of time during which anything exists. It was proposed that the duration of Parliament should be limited. Macaulay. Soon shall have passed our own human duration. D. Webster.
Shades of meaning
Fernald has no entry of its own for duration; he lists it under time.
Where he writes about it:
Sequence and succession apply to events viewed as following one another; time and duration denote something conceived of as enduring while events take place and acts are done. — from time
Duration and succession are more general words than time; we can speak of infinite or eternal duration or succession, but time is commonly contrasted with eternity. — from time
Time is measured or measurable duration. — from time