Are there tuning parameters that don't take effect immediately?

Last night I was doing some tuning on a database The longest query I was
running was taking around 160 seconds. I didn't see much change in the
running time for that query, even after restarting PG.

Today, with roughly the same system load (possibly even a bit heavier
load), that query is running about 40 seconds.

Are there tuning parameters in postgresql.conf that don't take effect right
away, even after a restart of PG? The only thing I can come up that's
happened since last night was that we ran the nightly vacuum analyze on
that database, but I did not change the statistics target.

The parameters I was working with were:

effective_cache_size
shared_buffers
temp_buffers
work_mem
maintenance_work_mem

Looking at the free command, I see a lot more memory being used for
buffer/cache today. (Centos 7.)
--
Mike Nolan
nolan(at)tssi(dot)com