In my current setup, I think my reverse proxy does not detect certificate updates (done by a different service), and I am just lucky that usually the service restarts because of some update before the old one expires.

Once that is solved, I am tempted to try the six-day expiration.

Did you consider the DNS-PERSIST-01 ACME challenge? You have to add a persistent TXT entry to your DNS, and then you are independent from provider support for renewals.