unsigned long time0 = 0;
unsigned long time1 = 0;
int threshold = 350;

void setup() {
  Serial.begin(115200);
}

void loop() {
  if (analogRead(A0) > threshold) {
    time0 = micros();
  }
  if (analogRead(A1) > threshold) {
    time1 = micros();
  }
  if (time0 && time1) {
    if (time1 > time0) // time0 was first
      Serial.println(time1 - time0);
    else // time1 was first
      Serial.println(time0 - time1);
    time0 = 0; time1 = 0; // reset times
    delay(250); // avoid ringing 
  }
}