Open the animation panel and notice the keyframes for your animation.  You have some buttons in the upper right part of the keyframes tab in that panel for changing the type of transition that is calculated between keyframes.  Default is spline and there is always a keyframe at frame 1 by default, so if you add a keyframe later on, you get this transition between frame 1 and the new keyframe.  If you want to keep the hand still for this time, you can change the transition between keyframes to constant instead of spline.  What you often have to do is copy the keyframe from the start of the still period to the end of the still period and then set the transition between them to constant.

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