Unexpected behavior when setting "idle_replication_slot_timeout"

Hi all,

I am exploring the new setting "idle_replication_slot_timeout" in Postgres
18; for testing purposes, I set the value to "30s", which, unexpectedly to
me, didn't cause an idle slot to be invalidated when I triggered a
checkpoint after the timeout had been reached.

The docs of the option state that the value is rounded up or down to the
nearest full minute, so I reckon "30s" gets rounded down to 0, thus
effectively disabling the feature. It might be less surprising to users if
values between "1s" and "59s" get actually always rounded up to one minute?
Arguably, that'd seem the more intuitive behavior to me. Alternatively,
logging a warning might be considered for values between "1s" and "30s"?
Curious what folks here think.

Thanks and all the best,

--Gunnar