I have a cron job for my sitemap but my question is,what is the better time for the cron job,is every 5 min?please help me,this cron job is for update my sitemap in google webmaster
You need to do it as often as there is any content change but not more often than Google is getting your sitemap. If you have lots of changes you can generate a new sitemap file every hour or so and add it to a larger sitemap index.