A continuously variable valve duration system including a rocker assembly acted upon by two off-spaced camshafts for selectively varying the closing point of a valve in an internal combustion engine. An opening camshaft is rotatably driven by the engine crankshaft and controls at least the opening and point of the valve through a rocker assembly disposed on a fixed pivot shaft. A closing camshaft, rotatably connected to the opening intake camshaft through a cam phaser, is poised to take over control of the valve closing event through the same rocker assembly. By changing the rotational phase of the closing camshaft relative to the opening camshaft via the cam phaser, the valve closing event can be either retarded or advanced so as to override the opening camshaft and thus selectively vary the valve event duration.