def round(unit = :sec)
      next_unit = self.ceil(unit)
      this_unit = self.floor(unit)
      (self - this_unit) < (next_unit - self) ? this_unit : next_unit
    end
def round(unit = :sec)
      next_unit = self.ceil(unit)
      this_unit = self.floor(unit)
      (self - this_unit) < (next_unit - self) ? this_unit : next_unit
    end
Returns a new Time representing the start of the current or next unit specified (second by default) depending which is closest