[UltraSane]

No, they will never get that short due to reliability issues. I could see getting down to maybe two weeks.

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.

[jaas]

Let’s Encrypt has already started issuing a limited number of 6-day certs and they will be generally available later this year.

(90 days will remain the default though)