Looking at the relevant limit, "Consecutive Authorization Failures per Hostname per Account"[0], it looks like there's no way to hit that specific limit if you only run once per day.
Ah, to think how many cronjobs are out there running certbot on * * * * *!
[0]: https://letsencrypt.org/docs/rate-limits/#consecutive-author...
I hope they don't go any shorter than a month. Let the user pick, any value up to a year should do.
To make 24 hour valid certs practical you would need to generate them ahead of time and locally switch them out. This would be a lot more reliable if systems supported two certs with 50% overlapping validity periods at the same time.
(90 days will remain the default though)
Incidentally the fact that it took them 4 days to respond to that issue is why I'll be wary of getting 6-day certs for them. The only reason it wasn't a problem there was that it was a 30d cert and had plenty of time remaining, so I was in no rush. (Also ideally they'd have a better support channel than an open forum where an idiot "Community Leader" who doesn't know what he's talking about wastes your time, as happened in that thread.)
SES? Around $0.0001 per e-mail
For a free service, that's a whole lot of money.
It's very under-engineered, maybe a trifold pamphlet on light A11 printed with a laser jet running out of ink.
I've probably spent more time talking about how much it sucks than I have bothered considering a proper solution, at this point.
I respect this. Reading someone else write this makes me feel more comfortable thinking about the things in my life I could be doing more to improve, which makes me respect this even more.