def stringify_times(obj)
      case obj
      when Hash
        Hash[obj.map { |k,v| [k, stringify_times(v)] }]
      when Array
        obj.map { |v| stringify_times(v) }
      else
        iso_format_time(obj)
      end
    end
def stringify_times(obj)
      case obj
      when Hash
        Hash[obj.map { |k,v| [k, stringify_times(v)] }]
      when Array
        obj.map { |v| stringify_times(v) }
      else
        iso_format_time(obj)
      end
    end
Recursively ISO format all time and date values.

 @param [Hash] obj the object containing date or time objects
 @return [Hash] the object with ISO-formatted time stings