How can I make a timer that go faster every second?

Not sure if this is what you want exactly, but it should give you a good idea how to write whatever it is you're trying to do.

     //timer = the clock, timerVal = how much the clock increases per second, increment = how much timerVal increases perSecond
     public float timer, timerVal, increment;
 
     //counts real time-seconds
     float secondCounter;
 
     void Update()
     {
         //if secondCounter has reached one-second or more
         if (secondCounter >= 1f)
         {
             //add to the clock
             timer += timerVal;
             //add to timerValue
             timerVal += increment;
             //reset secondCounter
             secondCounter = 0f;
         }
 
         //add to secondCounter the time that has passed since the last frame
         secondCounter += Time.deltaTime;
     }