Detect input, return true for 3s then return false

Basically I started scripting for the first time yesterday and want to detect a button input, "down", that returns a value ,true, for a given amount of time (roughly 2 seconds). This is so that an animation can play all the way through once it's triggered by the true value rather than stopping after a split second.

the code is:

 //A custom Controller for a side scrolling character, Horizontal for back and forth, vertical for look/aim up down, button for jump, crouch, action
 
 var speed : float = 3.0;
 var jumpSpeed : float = 6.0;
 var gravity : float = 20.0;
 
 // Back and forward movement code
 
 private var moveDirection : Vector3 = Vector3.zero;
 
 function Update(){
 
     var horizmove : float = Input.GetAxis("Horizontal");
      
             Debug.Log(horizmove);
 
     var controller : CharacterController = GetComponent(CharacterController);
     if(controller.isGrounded) {
     
             moveDirection = Vector3(0,0,Input.GetAxis("Horizontal"));
             moveDirection *= speed;    
 
                 
                     if(Input.GetButton ("Jump")) {
                         moveDirection.y = jumpSpeed;
                     }
                 }
                 moveDirection.y -= gravity * Time.deltaTime;
                 controller.Move(moveDirection * Time.deltaTime);
                 
     
     animator = GetComponent(Animator);
     
     var charwalkspeed : float;
     
         GetComponent(Animator);
         
             charwalkspeed == "Walkspeed";
             
             animator.SetFloat("Walkspeed",horizmove);
             
 //Turn around on button press code
 
     var pressturnbutton : boolean;
         
         if(Input.GetButton ("Downbutton")) {
             pressturnbutton = true; 
         }else{
             pressturnbutton = false;
         }
         animator.SetBool("PressTurn",pressturnbutton);
 
 }