// Declare as volatile any blinkDelayiables that you modify
// within the interrupt function.
volatile int blinkDelay;
static unsigned long past; // milis
unsigned long now;         // milis

void setup() {

pinMode(2, INPUT_PULLUP);
pinMode(3, INPUT_PULLUP);
pinMode(6, OUTPUT);

//LOW to trigger the interrupt whenever the pin is low
//CHANGE to trigger the interrupt whenever the pin changes value
//RISING to trigger when the pin goes from low to high
//FALLING for when the pin goes from high to low
attachInterrupt(digitalPinToInterrupt(2), green_button, FALLING);
attachInterrupt(digitalPinToInterrupt(3), red_button, FALLING);

Serial.begin(9600);
Serial.println("BEGIN");
Serial.println();

blinkDelay=500;

}

void loop() {

 Serial.println(blinkDelay);

 now=millis();
 if (now-past>=blinkDelay) {
 digitalWrite(6, !digitalRead(6));
 past=now;
}

}

void green_button() {
  blinkDelay=500;
  Serial.println(blinkDelay);
}

void red_button() {
  blinkDelay=3000;
  Serial.println(blinkDelay);
}