> 6 days means on a long enough enough timeframe the load will end up evenly distributed across a week.

people will put */5 in cron and result will be same, because that's obvious, easy and nice number.

I'd have it renew Monday and Thursday to avoid weekend outages.

ACME doesn't renew certificates when there's enough time, so it'll always renew around 6 days, even if you check more aggressively.

Currently ACME sets its cron job to 12 days on 90 day certificates.