Countdown Timer

//Create timeText in Hierarchy,
//in game manager.cs

public TextMeshProUGUI timeText;
    private float timeDown = 30;

    public void UpdateTime()
    {
        if(isGameActive)
        {
            timeDown -= Time.deltaTime;
            timeText.text = "Time: " + Mathf.Round(timeDown);
            if(timeDown <= 0)
            {
                GameOver();
            }
        }
    }

    private void Update()
    {
        UpdateTime();
    }