Trying to do my own timer function. I was wondering if there is any other ways to make my code more efficient without the use of a library. I noticed if I only use one timer function, I wont have multiple instances of the timer. My current code works though.

unsigned long previousMillis1 = 0;
unsigned long currentMillis1 = millis();
unsigned long previousMillis2 = 0;
unsigned long currentMillis2 = millis();
unsigned long previousMillis3 = 0;
unsigned long currentMillis3 = millis();

bool timer1(int preset){
  unsigned long currentMillis1 = millis();
  
  if(currentMillis1 - previousMillis1 >= preset ){
    previousMillis1 = currentMillis1;
    return true;
  }
  else{
    return false;
  }
}

bool timer2(int preset){
  unsigned long currentMillis2 = millis();
  
  if(currentMillis2 - previousMillis2 >= preset ){
    previousMillis2 = currentMillis2;
    return true;
  }
  else{
    return false;
  }
}

bool timer3(int preset){
  unsigned long currentMillis3 = millis();
  
  if(currentMillis3 - previousMillis3 >= preset ){
    previousMillis3 = currentMillis3;
    return true;
  }
  else{
    return false;
  }
}

void setup() {
 Serial.begin(9600);
}

void loop() {
  if(timer1(1000)){Serial.println(1);}
  if(timer2(2000)){Serial.println(2);}
  if(timer3(3000)){Serial.println(3);}
}