Using the same button for Jump and Levitate

I want to be able to use space bar to Jump, then again in the air to levitate. The Jump uses unity standard assets first person controller. The Levitate so far just uses:

if (Input.GetButton("Jump")) { m_MoveDir.y = 0; }

However, the GetButton is called before the player can release the space bar after using GetButtonDown to Jump. How do I create a delay before GetButton will register after GetButton Down?

More Code:

private void Update()

     {
         RotateView();
         // this is to prevent "pre jumping"
         m_Jump &= m_CharacterController.isGrounded;

         // the jump state needs to read here to make sure it is not missed
         if (!m_Jump)
         {
             m_Jump = Input.GetButtonDown("Jump");
         }


         if (!m_PreviouslyGrounded && m_CharacterController.isGrounded)
         {
             PlayLandingSound();
             m_MoveDir.y = 0f;
             m_Jumping = false;
         }

         if (!m_CharacterController.isGrounded && !m_Jumping && m_PreviouslyGrounded)
         {
             m_MoveDir.y = 0f;
         }

         m_PreviouslyGrounded = m_CharacterController.isGrounded;
     }


     private void FixedUpdate()
     {
         float speed;
         GetInput(out speed);
         // always move along the camera forward as it is the direction that it being aimed at
         Vector3 desiredMove = transform.forward*m_Input.y + transform.right*m_Input.x;

         // get a normal for the surface that is being touched to move along it
         RaycastHit hitInfo;
         Physics.SphereCast(transform.position, m_CharacterController.radius, Vector3.down, out hitInfo,
                            m_CharacterController.height/2f, Physics.AllLayers, QueryTriggerInteraction.Ignore);
         desiredMove = Vector3.ProjectOnPlane(desiredMove, hitInfo.normal).normalized;

         m_MoveDir.x = desiredMove.x*speed;
         m_MoveDir.z = desiredMove.z*speed;


         if (m_CharacterController.isGrounded)
         {
             m_MoveDir.y = -m_StickToGroundForce;

             if (m_Jump)
             {
                 m_MoveDir.y = m_JumpSpeed;
                 PlayJumpSound();
                 m_Jump = false;
                 m_Jumping = true;
             }
         }
         else
         {
             m_MoveDir += Physics.gravity*m_GravityMultiplier*Time.fixedDeltaTime;
         }

         //LEVITATE FUNTION
         if (Input.GetButton("Jump"))
         {
             m_MoveDir.y = 0;
         }

         m_CollisionFlags = m_CharacterController.Move(m_MoveDir*Time.fixedDeltaTime);

         ProgressStepCycle(speed);

         m_MouseLook.UpdateCursorLock();
     }