Slight modification of the Arduino Blink sketch

BlinkTwo

/*
  BlinkTwo
  Turns two LEDs on and off in unison.
  The delay times are controlled by two variables 
  that are defined at the beginning of the program. 
 
  This example code is in the public domain.
 */
 
// Use the LEDs that are connected to I/O pins 12 and 13

int led1 = 12;
int led2 = 13;

// Set delay values for the amount of time the LEDs 
// are on and the amount of time they are off.

int onTime = 100;
int offTime = 250;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pins as outputs.
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led1, HIGH);   // turn the LED on
  digitalWrite(led2, HIGH);
  delay(onTime);               // wait for a bit
  digitalWrite(led1, LOW);    // turn the LED off
  digitalWrite(led2, LOW);
  delay(offTime);               // wait for a bit
}