Plpgsql Question

Hello,

I'm new to Postgresql and plpgslq. I wrote a plpgsql to return epoch time
from a table, but had problem running it. The error returned:

NOTICE:  Error occurred while executing PL/pgSQL function sleeptime
NOTICE:  line 10 at assignment
ERROR:  Bad timestamp external representation 'rec_runtime.runtime'

My plpgsql function:

create function sleeptime () returns float as '
declare
        rec_runtime record;
        ret_sleepsecs float;
begin
        select into rec_runtime runtime from mon_nextrun order by runtime
limit 1;
        if rec_runtime.runtime is null
        then
            return 60;
        end if;
        ret_sleepsecs := extract (epoch from timestamp
''rec_runtime.runtime'') as float;
        return ret_sleepsecs;
end;
' language 'plpgsql';

What is the correct syntax for extract function in the assignment statement?

Thanks in advance.

-CT