How can I perform every 30minutes my Webalizer?

You can do that as a cron job...

crontab -e

however... I would highly recommend against it.. as the webalizer can become very processor intensitve..
I can't imagine why anyone would want that kind of timely stats..

If you are running a couple sites on the server and it's not really used as a shared hosting environment then go for it, otherwise don't do it - your server load will skyrocket every 30 minutes slowing things down.