public static int secondsInMinuteOf(long duration) {
        return (int) (duration - hoursOf(duration) * MILLIS_PER_HOUR - minutesInHourOf(duration) * MILLIS_PER_MINUTE) / MILLIS_PER_SECOND;
    }
Calculates the number of seconds within the specified duration excluding full minutes.

@param duration duration in milliseconds
@return number of seconds within the specified duration.
android/third_party/time-duration-picker/src/main/java/mobi/upod/timedurationpicker/TimeDurationUtil.java