This FAQ will explain domain name propagation
This answer will explain what propagation is, and how it will affect your domain after it is registered or transferred between providers.
'DNS propagation' is a term to describe the updating of information across the Internet. It takes two forms: changes to your DNS Zone and changes to your WHOIS information.
A change to your DNS Zone information typically affects only a handful of servers, and completes much more quickly. However, the WHOIS is the master record which tells every DNS server in the world the server for your domain. A change to your WHOIS information (such as updating the ADMIN-C in your control panel) can take up to 72 hours to propagate fully.
Customers often call the 123-reg support centre to say that they can't see their domain names straight after ordering them, or just after a transfer between providers. After either of these two events your domain name/website may not be visible for up to 48 hours, mainly because millions of DNS servers need to be updated with the new information.