Try extending that time to 10 seconds.  Three seconds is very fast for that motion.  IIRC, the frame counter is in actual seconds but I would need to verify that information from the manual.  Setting the number of frames from 1 to 10 should be sufficient time to see how the model responds to the poses.  Frame 1 is your starting pose, frame 10 is your ending pose, and frame 5 should be your intermediate pose with the arms out front.  Frame 5 is the point that needs to be keyframes.  You could simply reposition the arms at frame 5 without keyframing, I think Poser will internally interpret the change especially if it's going to be an up-and-down motion.  The keyframing will come into play if you raise the arms and hold them in that position for an extended period of time.