Changing conf file automatically

I was recently asking about restricting access to certain sites
(webmail) to particular IP addresses on site. Thanks to the help
from here I have that working. I have now been asked to vary this
and allow more machines access at lunch time only. Could I use a
cron job to re-copy the conf file from a master copy and then
restart (kill -HUP ???) squid? I have never created a cron job, am
sure I can do it through Webmin but am totally unsure what
commands to enter.

Any help appreciated.
Cheers

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Simon Bryan                    sbryan@olmc.nsw.edu.au
Information Technology Manager sbryan@mpx.com.au
OLMC Parramatta