Do not hardcode \timing on

[rominf]

Make it option for your plugin.

And also I recommend you to wrap such actions to:

\set QUIET on
...actions...
\set QUIET off

to get rid off unwanted messages ("timing enabled", "pager enabled", etc.)

[ivalkeen]

Added g:simpledb_show_timing to make timing optional

Regarding unwanted messages, the easiest way to avoid them is adding -q flag to connection line.