I am not saying 6 days is long enough, but if your automation always wait until the last minute to renew certs, you may have more issues to worry about than the CA's availability. If I am going to use a cert with 6 days lifetime I will be renewing it at least once a day.
If you have multiple hosts the set should not be the same, no? From the linked page the comparison is a set comparison: one host at hosta.example.com and one host at hostb.example.com each with their own cert bot won't conflict.