Handling Animation and movement speed

Hello, i am currently working on an interactive instalation in unity. It features a creature like a medusa, during the movement animation the speed is not linear in a sense that when it's flap "closes" it has to move faster than when it is "opening". I tried to isolate the frames by adding a framecounter, but as it has more than 1 animation and the transition between animations is quite tricky the framecounter gets a progressive delay All this is tied to 3D random movement trhough a rigid body logic.

i need a way to set the movement speed for only a specific window of the animation, is this possible?