code: public final int getOpenMinutes() {
          final HourRange hr = normalize().get(0);        
          return hr.to.toMinutes() - hr.from.toMinutes();
      }
docs: Returns the number of minutes the instance is 'open'.
  CAUTION: Minutes that overlap to the next day are ignored!
  This means '21:00-03:00' returns 180 minutes (and not 360).
  
  @return Minutes (1-1440)