Many of the changes you make have immediate effect. The ones that don't tend to involve DNS or domain registration changes.
Most DNS changes, such as associating a name like www.example.com with a site hosted here (by adding an alias), take effect within a minute or two. However, there is a catch. If you recently accessed the name before you set it up, your browser and/or local ISP may "remember" the old information. (Either that it pointed somewhere else or that it didn't work.) If you're moving things around on our system, it should be visible within a couple of hours. If you moved a domain over from somewhere else, it might take longer depending on their setup.
The time it takes to see DNS changes is controlled by the time-to-live (TTL) value for the relevant DNS records. (If a record doesn't exist, the domain contains a setting called Minimum TTL, which will be used to tell people how long they should assume that record will continue not to exist.) When you look up a domain name, your local name server (usually run by your ISP) will look at the TTL value and "remember" (cache) the answer for long, even if there are changes in the meantime.
The root DNS servers operated by the domain registries store your name server records with TTLs of two days. That means if you change your domain's name servers, that change can take up to two days to be fully visible throughout the Internet. (The same applies if your domain expires and gets the expired "parking" name servers, so don't let that happen!)
For a newly-created domain name, things will often work within a few minutes if you don't try to see if it's working until it's already working. If you happen to hit it before it's ready, you'll trip the DNS TTL delay and may have to wait a bit longer. If it's not working after an hour or so, check for configuration issues with your site, DNS records, or nameserver settings.
You should always be able to see a new site using our nfshost.com domain within a few minutes.