class ActionView::Helpers::Tags::DatetimeField

def datetime_value(value)
  if value.is_a? String
    DateTime.parse(value) rescue nil
  else
    value
  end
end

def format_date(value)
  value.try(:strftime, "%Y-%m-%dT%T.%L%z")
end

def render
  options = @options.stringify_keys
  options["value"] ||= format_date(value(object))
  options["min"] = format_date(datetime_value(options["min"]))
  options["max"] = format_date(datetime_value(options["max"]))
  @options = options
  super
end