Let's break this into 2 parts:
1) VPS the provision is automatic so when you finish paying for the VPS it is there for you to use, also we use Virtualzor as a control panel so clients do not matter if is OpenVZ or KVM will have a button on his control panel to choose and install at one click, cPanel, Webmin, VestaCP, Plesk, Interworks, Centos Web Panel, Webuzo, and ISPConfig3. All this just a click, see picture.
Dedicateds are different:
1) if it is not pre-configured need to know what customer wants to install inside so it is build to order and takes a long time also need to rack connect Network and install OS desired, it can take about 1 to 3 days depending on the provider.
2) Pre-configured means that the only thing that you choose is the OS to be installed or you can install it yourself through a KVM/IP it's a little faster but also depends on the provider also can take for 1 to 3 days.
Hope this answers your question.