Cooldown/Countdown not working as expected

Hi!

I´ve made a script for my ingame BulletTime Feature. It´s working fine. I figured out, that it´s neat for the Player to recognize, when the BulletTime is ready again. The problem is: The way I built it, it only tracks the remaining available BulletTime and completely ignores the Cooldown I made for the BulletTime itself.

The way it is working: I activate BulletTime and an ingame Symbol disappears while BulletTime is active. If all BulletTime is used or if the player pauses BulletTime the ingame Symbol reappears.

BulletTime available is 3 Seconds. The overall Cooldown on BulletTIme if the 3 seconds are used is 10 Seconds.

The part which might confuse the player is: The symbol reappears after the 3 seconds, but he can´t use BulletTime, because the overall cooldown is still running.

Is there a way to track the overall cooldown for the BulletTime separately? I tried coroutines, IEnumerators. GUI CountdownTrackers (neat, but if you combine it with the same Keyboard Input, you have to press the button for every single second counted down or I don´t get how CountdownTrackers work).

I hope this isn´t too confusing overall.

Tl,dr: I´m searching for a way to combine two separate timers in one displayed object(or add a second displayed timerobject which is aible to keep track with the first one)

Thanks in advance.

     public float currentBulletTimer   = 0f;
 public float bulletTimeAllowed = 3.0f;

 public float timeBetweenBulletTime =0.3333f; 
 private float timestamp;

 public GameObject BulletTimer;
 //private Coroutine Timer;
 // Use this for initialization
 void Start () {
     
 }
 
 // Update is called once per frame
 void Update () {
     if (Time.time >= timestamp && (Input.GetKeyDown(KeyCode.U)))
     {
         if(Time.timeScale == 1.0f)
             Time.timeScale = 0.3f;
         else
             Time.timeScale = 1.0f;
         BulletTimer.SetActive(true);
     }

     if(Time.timeScale == 0.3f)

     {
         currentBulletTimer += Time.deltaTime;
         BulletTimer.SetActive(false);
     }

     if(currentBulletTimer > bulletTimeAllowed)

     {
         currentBulletTimer = 0f;
         Time.timeScale = 1.0f;
         timestamp = Time.time + timeBetweenBulletTime;
         BulletTimer.SetActive(true);
     }

} }