How do I get my timer to start in my start function instead of update()

using UnityEngine;
using Spine.Unity;
using Spine;
using UnityEngine.SceneManagement;

public class DoorTransition : MonoBehaviour
{

    public SkeletonAnimation SkelAnim;

    [SpineAnimation]
    public string DoorClose;
    bool TimerStarted = false;
    private float _timer = 0f;
    public float LoadLevelDelay = 1f;


    void Awake()
    {
        SkelAnim = GetComponent<SkeletonAnimation>();
    }


    private void StartDoor()
    {
        TimerStarted = true;

        SkelAnim.state.SetAnimation(0, DoorClose, false);
        }

    

    void Update()
    {
        if (TimerStarted)
        {
            _timer += Time.deltaTime;

            if (_timer >= LoadLevelDelay)
            {
                SceneManager.LoadScene("LevelOne");
            }

        }
    }
}