There could be a few reasons.
Since it’s the animation playback it could be an offset introduced as part of the ease in and ease out component so if you set these values to zero then the state should change with in the cycle with out the need for the blended time. Action states, involving the arms, generally don’t require ease in and ease out unless the key pose change is dynamic like a equip un-equip.
If still offset
Key types can vary from application to application as to how Bezier curves are imported and is a common problem. This occurs between set key frames like starting at 0…5…10…15 and allowing the curve interpolation drive the animation. The way to solve it is to bake all of the frames out so that the animation occurs on the frame and not just the key frame alone
In 3DS Max at export by selection that would be Extra Options > Bake Animation and check Bake Animation and set the range