int Time_second;
int Time_minute;
int Time_hour;

long Time_hour_setting = 3600000;
long Time_minute_setting = 60000;
long Time_second_setting = 1000;

unsigned long start_time;


void setup() {

  Serial.begin(9600);

}

void loop() {

  start_time  = millis();

  Time_hour = start_time / Time_hour_setting;                                                       //開始時間除以小時
  Time_minute = (start_time % Time_hour_setting) / Time_minute_setting;                             //開始時間除以小時再除分鐘
  Time_second = ((start_time % Time_hour_setting) % Time_minute_setting) / Time_second_setting;   //開始時間除以小時再除分鐘再除秒

  Serial.print(Time_hour);
  Serial.print(":");
  Serial.print(Time_minute);
  Serial.print(":");
  Serial.println(Time_second);
}