If your account key is associated with a valid authorization for your FQDN and that authorization is valid for at least another 24 hours, the CA server does not generate a new authorization (with a new expiration date), but rather reuses the existing one (in order not to have tons of unnecessary database rows with authorizations for the same FQDN).
This is independent from the certificate expiration date; that one's still 90 days from the date of issuance either way, even if the authorization might have expired by then. It just has to be valid (and non-expired) at the time of issuance.
This was implemented back in June, see the full announcement here: