Time

millis()

millis

Returns the number of milliseconds since the device began running the current program. This number will overflow (go back to zero), after approximately 49 days.

unsigned long time = millis();

// EXAMPLE USAGE
SerialLogHandler logHandler;

void setup()
{
}

void loop()
{
  unsigned long time = millis();
  //prints time since program started
  Log.info("millis=%lu", time);
  // wait a second so as not to send massive amounts of data
  delay(1000);
}

Note: The return value for millis is an unsigned long, errors may be generated if a programmer tries to do math with other data types such as ints.

Instead of using millis(), you can instead use System.millis() that returns a 64-bit value that will not roll over to 0 during the life of the device.