https://docs.renovatebot.com/key-concepts/scheduling/#deprecated-breejslater-syntax says the wordy Later.js syntax is deprecated:

This section explains the deprecated @breejs/later syntax. We plan to remove the @breejs/later library in a future major Renovate release if we can find a way to migrate all valid schedules to cron syntax. Due to this upcoming change, we strongly recommend you use cron schedules.

https://docs.renovatebot.com/key-concepts/scheduling/#recommended-cron-syntax says:

For Cron schedules, you must use the * wildcard for the minutes value, as Renovate doesn't support minute granularity. And the cron schedule must have five parts.

https://crontab.guru/#*_*_3__ says * * 3 * * is:

“At every minute on day-of-month 3.”