There is a “pre-boot” script that runs before all the built-in Zeroshell scripts. You can use it to set up special hardware, patch the Zeroshell scripts, etc.
There is a “post-boot” script that runs after all the built-in Zeroshell scripts. You can use it for what ever. That might be a reasonable place to setup up your cron job(s). You can place your custom scripts in the /Database directory and they will be persistent across reboots.