That depends on who you registered it with.
Some registrars will register your domain immediately in a totally automated manner. In these cases, your domain is registered already.
Others will manually process your "domain registration application" after they have validated your credit card and gotten around to the task of manually submitting the registrations.
This could be done in minutes, hours, days or even weeks I support in the case of someone sleeping at the switch
I would suggest you contact the registrar you used and ask them.