Deactivate Object Between 15-45 Seconds Of Not Visible

Like the title says, is there a way to deactivate an object randomly between a given time? I know there's something like OnBecameVisible but is there an OnBecameInvisible or something like that?
**EDIT**
After some messing around i managed to do something but is there a way to fade the audio out from the audio source I attached (not referenced in script).
Code

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class ChaseDeactivate : MonoBehaviour
6. {
7.     [SerializeField]
8.     private float delayBeforeLoad;
9.     [SerializeField]
10.     public GameObject killerObj;
11.     private float timeElapsed;
12.  
13. void Start()
14. {
15. delayBeforeLoad = Random.Range(15.0f, 45.0f);
16. }
17. private void Update()
18. {
19. timeElapsed += Time.deltaTime;
20.  
21.  
22. if (timeElapsed > delayBeforeLoad)
23. {
24. Destroy(killerObj);
25. }
26. }
27. }
28.  

 

Starting a Coroutine that fades audio, then disables the gameObject when done. If I remember correctly it's faster to change the gameobjects visibility and disable scripts than it is to disable the gameObject entirely ( Haven't been using Unity as much recently )

 

oh ok thanks