時間経過でDestroy

TimeDestroy.cs

using System.Collections;
using UnityEngine;

public class TimeDestroy : MonoBehaviour
{
    [SerializeField]
    private float destroyTime = default(float);
    private float start;

    private void Start()
    {
        start = Time.time;
    }

    private void Update()
    {
        if(destroyTime < Time.time - start)
            Destroy(this.gameObject);
    }

    public void SetTime(float time)
    {
        destroyTime = time;
    }
}