Simple serial controllable timer using relay

relay_timer.ino

int timer;
String buffer;
int relay = 7;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  while (!Serial) {
    ; // Wait for serial port to connect
  }
  pinMode(relay, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if (Serial.available() > 0) {
    switch (Serial.read()) {
      case 'T':
        buffer = Serial.readStringUntil('\n');
        timer = buffer.toInt();
        digitalWrite(relay, HIGH);
        delay(timer);
        digitalWrite(relay, LOW);
        Serial.println("OK");
        break;
      case 'H':
        digitalWrite(relay, HIGH);
        Serial.println("OK");
        break;
      case 'L':
        digitalWrite(relay, LOW);
        Serial.println("OK");
        break;
    }
  }
}