void Update () {
  Debug.Log("123");
  yield WaitForSeconds(1);
  Debug.Log("OK");
                //еще какие-нибудь действия

    }

yield return new WaitForSeconds(1);

void Update()
{
StartCoroutine(Example());
}

IEnumerator Example() {
        Debug.Log("123");
        yield return new WaitForSeconds(1);
        Debug.Log("OK");              
    }
    

float StartDelay = 5f;
float Delay = 5f;

void Start()
{
this.Delay = this.StartDelay;
}

void Update()
{
this.Delay -= Time.deltaTime;
if(this.Delay > 0) return;
Debug.Log("Tick!");
this.RefreshDelay()
}

void RefreshDelay() {
this.Delay = this.StartDelay;
}