Diagnostic

I am trying to determine how many seconds a query takes, and I can't
figure it out.  I seem to remember some weird, mostly undocumented query
that went like:

foo# get diagnostics select processed into <int4 variable>;
foo# show <int4 variable>;

But this doesn't work, and I think it may only work in plpgsql function
anyway.

I know how to use explain, but I want to see if postgres is correct
which query is fastest.

Does anybody know how to find this info out?

Thx