OK so I asked HostGator customer support why my subdomains take time to show up after creating them in cPanel. (I go into cPanel and create a new subdomain but it won't show up for me when I load the page in the browser).
They informed me that it takes 4-8 hours for subdomain creation within cPanel / WHM. It doesn't matter if I go with Shared Host, VPS, or a private host - they will always take that amount of time to propagate. Is this only a case with HostGator? I was under the impression that new subdomains should be up and running instantaneously?