bash: homemade timeout replacement

So I was young and reckless, and didn't know there is a command called timeout in coreutils. This is how I managed to do it:

#!/bin/sh
{
    ./time_consuming_binary -a param -a notherparam --pleaseblock
} &
CHILDPID=$!
# Kill it after 30 sec
sleep 30
kill -9 $CHILDPID 2>&1 /dev/null

How to check if it had to be killed or not? Measure the wall time of the execution :) I've used it in a Nagios service check, the thing it watched either returned under 5 sec or blocked indefinitely (thanks, NFS), hence the 30 secs.