running a script only till a point in a day

Shell Programming and Scripting
1

how can i run the script if its less than a particular time only in unix.

for e.g the script kicks off at 9AM and looks for some file etc. I want to make sure it runs only till 12PM and then succeed the job and proceed regardless if the file exists or not. how can we do this

2 
echo waiting ...
while true
do
        date
        test `date '+%H:%M'` == "12:00" && echo time is up && break
        test ! -f /tmp/x.x && echo file not found, sleeping ... && sleep 10
        test -f /tmp/x.x && echo file has been found && break
done
echo done

Tested on Cygwin and OpenBSD