You can of course set the cron job to only run every 5 minutes, as we cannot override that, but we do specify one minute for a variety reasons. If you are the only one ever posting on your site, it probably won't matter.
Just FYI, I've used the EasyCron service in the past when faced with the same issue of a 5-minute minimum. It only cost about $8 a year, their lowest-cost tier, but allowed 1-minute cron jobs. Something to consider, anyway. 🙂