The plot time range determines when a plot appears or disappears in a keyframed animation. Since VisIt allows plots to exist over a subset of the animation frames, you can set a plot's plot range in the Keyframe area to make a plot appear later in an animation or be removed before the animation reaches the last frame. You may find it useful to set the plot range if you've increased the number of animation frames but found that the plot range did not expand to fill the new frames. To change the plot time range, you left-click on the beginning or ending edges of the Plot time range (the green band on the Keyframe line) in the Keyframe area and drag it to a new animation frame.