This sounds like a very good thing, like a lot of stuff coming from letsencrypt.
But what risks are attached with such a short refresh?
Is there someone at the top of the certificate chain who can refuse to give out further certificates within the blink of an eye?
If yes, would this mean that within 6 days all affected certificates would expire, like a very big Denial of Service attack?
And after 6 days everybody goes back to using HTTP?
Maybe someone with more knowledge about certificate chains can explain it to me.
With a 6 day lifetime you'd typically renew after 3 days. If Lets Encrypt is down or refuses to issue then you'd have to choose a different provider. Your browser trusts many different "top of the chain" providers.
With a 30 day cert with renewal 10-15 days in advance that gives you breathing room
Personally I think 3 days is far too short unless you have your automation pulling from two different suppliers.