SOLUTION
To create a cron job for a time that is not available in OpenVix GUI (i.e every half hour or anything else) the simplest way to do this is to use a FTP file manager such as Total Commander and edit the following file on your box,
Code:
/etc/cron/crontabs/root
enter your required time followed by the path to the script you would like to run, for example
Code:
*/2 * * * * /usr/scripts/script_name.sh
which will run the selected script every 2 mins.
It is useful to know the logs for cron jobs can be found at: A good website to help you set your cron job time exactly as you would like is: https://crontab.guru/
Thanks to user Birdman