Ruby では、これで設定できる

require 'inifile'

str = "Wed Aug 12 23:59:59 2020"

ini = IniFile.new( :filename => "test.ini" )

ini[ "abc" ] = { "LastCheck" => str, "LastUpdate" => str }
ini.write( ) # save

結果
[abc]
LastCheck = Wed Aug 12 23:59:59 2020
LastUpdate = Wed Aug 12 23:59:59 2020