Thank you very much for your reply.

Would you give me the instruction for the cronjob? Or is there any tutorial about it?
I am using the website Webcron to backup my website everyday using Akeeka. So I have a such service.

Another question for you. When I add an article or when I modify something in my website, the caches are cleaned automatically using a plugin. Is it a problem with Jsitemap pro? Does the extension has its own cache or the general one?

Thanks for your help
Amar Guillen