[C#] How to add some sort of timer?

So this is my code.

    void Update(){
    if(speedDirection >= 10f){
    			speedDirection += 100f;
    		}else{
    			++speedDirection;
    		}
}

How do I make the speedDirection to update at each second or else? Is there some sort of Timer to make the speedDirection increase or decrease by 1 every second?

Sorry for my english…

The easiest solution would be to use InvokeRepeating():

void Start() {
    InvokeRepeating("SpeedTest", 0.0, 1.0);
}

void SpeedTest(){
    if(speedDirection >= 10f){
             speedDirection += 100f;
           }else{
             ++speedDirection;
           }
}

If you want to repeat this forever, use InvokeRepeating:

void Start(){
  // call IncSpeed in one second and repeat every second:
  InvokeRepeating("IncSpeed", 1, 1); 
}

void IncSpeed(){
  if(speedDirection >= 10f){
    speedDirection += 100f;
  } else {
    ++speedDirection;
  }
}

Another option is to create your own timer:

float nextTime = 0;

void Update(){
  if (Time.time > nextTime){
    nextTime = Time.time + 1;
    IncSpeed();
  }
}

void IncSpeed(){
  if(speedDirection >= 10f){
    speedDirection += 100f;
  } else {
    ++speedDirection;
  }
}