static function Lerp(from: float, to: float, t: float): float;

using UnityEngine;
using System.Collections;

public class CameraAnimations : MonoBehaviour
{
public CharacterController playerChC;

float CameraCurrentAngleX;
float CameraCurrentAngleY;
float CameraCurrentAngleZ;
public AnimationClip Walking;
public AnimationClip Running;

void Update()
{
float ReturnTime = 10f;

CameraCurrentAngleX = transform.localEulerAngles.x;
CameraCurrentAngleY = transform.localEulerAngles.y;
CameraCurrentAngleZ = transform.localEulerAngles.z;

float RetutnCamPosX = Mathf.Lerp(CameraCurrentAngleX , 0f, ReturnTime );
float RetutnCamPosY = Mathf.Lerp(CameraCurrentAngleY , 0f, ReturnTime );

if (playerChC.isGrounded == true)
{
if (Input.GetKey(KeyCode.W) | Input.GetKey(KeyCode.A) | Input.GetKey(KeyCode.S) | Input.GetKey(KeyCode.D))
{
animation.CrossFade(Walking.name);
}
if (Input.GetKey(KeyCode.W) & Input.GetKey(KeyCode.LeftShift))
{
animation.Stop(Walking.name);
animation.CrossFade(Running.name);
}
}

if (Input.GetKeyUp(KeyCode.W) | Input.GetKeyUp(KeyCode.A) | Input.GetKeyUp(KeyCode.S) | Input.GetKeyUp(KeyCode.D))
{
animation.Stop(Walking.name);
if (CameraCurrentAngleX > 0 | CameraCurrentAngleY > 0 | CameraCurrentAngleX < 0 | CameraCurrentAngleY < 0)
{
transform.localEulerAngles = new Vector3(RetutnCamPosX, RetutnCamPosY, 0);
}
}
}
}

if(curXRot > 0) {  
  curXRot -= curXRot*Time.deltaTime;  
  }  
  if(curXRot < 0) {  
  curXRot += curXRot*Time.deltaTime;  
  }  
  if(curYRot > 0) {  
  curYRot -= curYRot*Time.deltaTime;  
  }  
  if(curYRot < 0) {  
  curYRot += curYRot*Time.deltaTime;  
  }
  }

var time1 : float = 5;
.....
curXRot -= curXRot*Time.deltaTime/time1;

curXRot -= Time.deltaTime/time1;