display processing time?

I have a question about how to display query time of  postgres.  I found 
this
postgres [ -A { 0 | 1 } ] [ -B buffers ] [ -c name=value ] [ -d
 debug-level ]
           [ -D datadir ] [ -e ] [ -E ] [ -f { s | i | n | m | h } ] [ -F ]
           [ -i ] [ -L ] [ -N ] [ -o file-name ] [ -O ] [ -P ]
           [ -s | -t { pa | pl | ex } ] [ -S sort_mem ] [ -W num ] database

adding -s will print the statistis and time. But I have no idea how to call 
this using postmaster -o option. Anyone give me a hint? Thanks.

-John