Your site becomes live when the DNS updates that you requested from Hostmaster go into effect, and your hostname(s) have been added to your Pantheon site dashboard. Hostmaster can schedule DNS updates upon request.
When you initially add your hostname(s) to your Pantheon site dashboard, and once the DNS changes go into effect, it can take up to one hour for the hostname(s) to finish HTTPS provisioning on Pantheon's Global CDN.
Once the updates are implemented, visiting your live hostname (EXAMPLE.berkeley.edu) from within the UC Berkeley campus network should take you to your new site.
It is possible that visiting your live hostname from a network other than the campus network will not take you to your live site right away. There can be a 2 hour to multi-day lag as for the DNS to propagate to other DNS servers. For more about DNS propagation, see What is DNS Propagation?. To monitor this progress you can use sites like https://www.whatsmydns.net/.