When you go into keyframing mode for the first time, having never set a number of keyframes, VisIt will use the number of states in the active database for the number of frames in the new keyframe animation. The number of frames in the keyframe animation will vary with the length of the database with the most time states unless you manually specify a number of animation frames, which you can do by entering a new number of frames into the Keyframing Window's Number of frames text field. Once you enter a number of frames, the number of frames will not change unless you change it.