This is probably a really dumb question, but I just registered a domain at Dreamhost. I wanted to edit the DNS settings, but its been over 12 hours, and whenever I go to manage domain, it just shows me my domain name, and no DNS/Add IP option. How long does it take for the DNS to show up?

Have you seen the Edit button in colum 3 under web hosting?
If it is not there, contact support.

You need to set up some sort of service before you get DNS entries. Either “Manage Email” or “Manage Domains” will do this. If you just want DNS, you can go to Manage Domains and Add New Domain/Subdomain. Scroll to the very bottom of the next screen for a DNS-Only domain. That should get you started.