Unity timer Question

First in my game, i have “Booster” the problem is. If i make timer with “Time.delaTatime” with float, it also affect to my game timer. Since i changed timeScale.
So my Question is
“Can i make timer without touch my stamina code?”
Player will die after the timer reaches 0.00f // 30f start → 0f → player die

public void Booster()
{
	isBoost = true;
}
void Update()
{
    public float stamina = 10f, maxstamina = 10f;
    public bool isBoost;
    public GameObject staminaBar;
    float myStamina = stamina / maxstamina;

	if (isBoost) 
	{
		Time.timeScale = 3f;
		stamina -= Time.deltaTime;
		staminaBar.transform.localScale = new Vector3 (myStamina, staminaBar.transform.localScale.y, staminaBar.transform.localScale.z);

		if (stamina < 0) 
		{
			stamina = 0.00f;
			isBoost = false;
			Time.timeScale = 1f;
		}
	}
	else if (stamina < maxstamina) 
	{
		stamina += Time.deltaTime;
		staminaBar.transform.localScale = new Vector3 (myStamina, staminaBar.transform.localScale.y, staminaBar.transform.localScale.z);

	}
}

So you have a variable time scale but want unscaled time for some calcs?
Use Unity - Scripting API: Time.unscaledDeltaTime ???