Here's a link I would send to my coworkers: https://crontab.guru/#30_2,10,18___*
This site, is one of several you could use. I have recommended this one because they said it makes sense. As they click to each number field, the help text changes, and they can learn how to build a cron timeframe on their own. A word of caution, while this site may help with a large amount of crons, it sometimes can't help with the very complex.
The cron expression you are looking for in this instance is: 30 2,10,18 * * * Go to the site to read about why that is the answer, and hopefully it can also help you in the future.
If this reply helps you, an upvote would be appreciated.