Scene change

if timer=20 , change other scene. I dont want collider or trigger.

That’s what you need, I guess.

using UnityEngine;
using UnityEngine.SceneManagement; // IMPORTANT!
using System.Collections;

public class SceneChanger : MonoBehaviour {

	float timer = 0;

	void Update() {
		timer += Time.deltaTime;

		if(timer > 20) {
			SceneManager.LoadScene(1);
		}
	}
}

Note that the parameter in LoadScene(param) is the buildIndex of the scene you want to load.

Yes its work!