timer.pde

int startTime;
int threshould = 3000;

void setup() {
  startTime = millis();
}

void draw() { 
  int diff = millis() - startTime;
  if (diff > threshould) {
    background(color(255, 0, 0));
  } else {
    background(color(0, 0, 255));
  }
}

void keyPressed() {
  startTime = millis();
}