Unity 5 - Easy Day/Night system
Hope this helps!
Here's the script if you don't want to write it.
using UnityEngine;
using System.Collections;
public class Example : MonoBehaviour {
// Use this for initialization
void Start () {
}
// Update is called once per frame
void Update () {
transform.Rotate (Vector3.up * Time.deltaTime * .5);
}
}