I can't get my script to work I get an error. [Please Help!]

My script I'm making is to make it so every 90 seconds my skybox automatically changes. (Basically my own nooby Day/Night cycle.)

But I keep getting this error: BCE0023:

No appropriate version of 'UnityEngine.Object.Destroy' for the argument list '(System.Type)' was found.

Here's my script please tell me what you think.

P.S I'm a noob to scripting please no harsh words. :)

var mat1:Material;

var mat2:Material;

var timer : float = 90.0;

function Start(){

RenderSettings.skybox=mat1; } function Update() { timer -= Time.deltaTime; if(timer <= 0) { timer = 90; night = true; }

 if(night == true)
 {
 RenderSettings.skybox=mat2;
 }
 
 if(night == true)
 
 timer -= Time.deltaTime;
 
 if(timer <= 0)
 {
     timer = 90;
     day = true;
 }
 if(day == true)
 
 {
 RenderSettings.skybox=mat1;
 }

}