How long does it take to add overdraft to your Sparkasse checking account?

Hi,

There are two ways to add an overdraft facility: online or by making an appointment with a bank advisor. What do you need for this? Employment contract, pay slips, etc.? It says that you can activate this option in your online banking system now, so I'm confused. Has anyone here had any experience with this? I actually want to pay my bills even though there isn't enough money in my checking account. At the moment I can't go into the red; I'm employed full-time.