The updates you make through our site update the registry in real time. However, this usually take 24-48 hours from the time of registry update to propagate around the web.
Well, the changes you make have to propagate through the 'Main Root Servers' and all the web servers around the world. These servers have caching periods, which means they only refresh their information on your domain's Zone File every so often.
As an example, when you connect to your site, you're probably connecting through 10-15 other servers or gateways, e.g. your ISP's exchange, then a couple more hops between the various cities etc. Each one of these servers must contain the correct information, it only takes one link in the chain that thinks your domain points to the old record to delay your recent update. This also explains why some people may be able to view your update, but not others (it's possible their path to your server has been updated with the correct information).