Solrのdateフィールドに入力する値のフォーマットについて

solr_datetime.rb

require 'rsolr'
require 'time'

mode = ARGV[0] || "1"

url = case mode
      when "1"
        "http://localhost:8983/solr/collection1"
      when "2"
        "http://localhost:8983/solr/collection2"
      end

solr = RSolr.connect :url => url

instances = case mode
            when "1"
              (1..5).map do |i|
                {
                  uri: "http://example.com/resource/#{i}",
                  label: "リソース#{i}のラベル",
                    description: "リソース#{i}の概要をここに書く",
                    last_modified: Time.now.strftime("%Y-%m-%dT%H:%M:%SZ-9HOUR"),
                    links: [
                      "http://example.com/link/from/#{i}/to/1",
                  "http://example.com/link/from/#{i}/to/2",
                  "http://example.com/link/from/#{i}/to/3",
                  ]
                }
              end
            when "2"
              (1..5).map do |i|
                {
                  id: "#{i}",
                  title: "id#{i}で識別されるリソースのタイトル",
                  body: "リソース#{i}の内容をここに書く",
                  last_modified: Time.now.strftime("%Y-%m-%dT%H:%M:%SZ-9HOUR"),
                }
              end
            end

solr.add(instances)
solr.commit