Nowhere in the blog post does it say they can't cope with the load, which is why the rate limits are so high. This is only about reducing wasted resources by blocking requests which are never going to succeed.
They definitely can't cope with the load at midnight, or at least couldn't back in 2022, and the fact that they mention midnight specifically in this post makes me assume they still can't. I say this because I had cert issuance fail for multiple days because of DB timeouts on their end from that: https://community.letsencrypt.org/t/post-to-new-order-url-fa...
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.)
