After your order has been placed for your chosen VPS and payment has been received your VPS normally takes around 2 hours before it is fully operational. Sometimes this can be much sooner.
Once your VPS has been set up and ready to use you will be emailed your login details which can be changed at any time.
Sometimes upon your first login you may get some notifications stating you need to reboot your server for either updates or to activate your cPanel should you choose cPanel to be installed.
Once this has been done you should not have any notifications. Reboot on a freshly installed server takes around 1 minute depending on your chosen location.