code: public static long systemTimeIntervalBetween(
              long earlierTime, long laterTime, TimeUnit systemTimeIntervalUnit) {
          long intervalNanos = laterTime - earlierTime;
          return systemTimeIntervalUnit.convert(intervalNanos, NANOSECONDS);
      }
docs: Returns system time interval (i. e. wall time interval) between two time values, taken using
  {@link #currentTime()} method, with the highest possible precision, in the given time units.
  
  @param earlierTime            {@link #currentTime()} result, taken at some moment in the past (earlier)
  @param laterTime              {@link #currentTime()} result, taken at some moment in the past, but later
  than {@code earlierTime} was taken ("later" means there is a happens-before relationship
  between the two subject {@code currentTime()} calls)
  @param systemTimeIntervalUnit the time units to return system time interval in
  @return wall time interval between the specified moments in the given time unit