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Let's Encrypt Announces New-Certificate-Every-6-Days Offering
(letsencrypt.org)
This is a most excellent place for technology news and articles.
The attack would only need to last for a day or two, and then everyone requesting updated certs when it stops could push enough people outside the 6-day window to cause problems. 6 days is probably long enough to not be a huge issue, but it's getting close to problematic. Maybe change to 15 days, which should avoid the whole issue (people could update once/week and still have a spare week and a day to catch issues).