macos - How can I write a cron job that will block my internet from 7pm to 7am? (So I can get some sleep)

I am using OSX 10.6 and it has cron built in. How can I write a cron job that will block my internet from 7pm to 7am every day?

Im sure this must be simple but I could only find one example online and it didn't work. It said to:

set /etc/hosts.allow file to 
be empty 
set hosts.deny file to
ALL : ALL

I did this and google still came up.