Windows update client -reboots inconvenient timing

When I boot my computer in the morning, more than once, Windows 7 shows a message by the systray that windows will reboot in so many minutes. If I don't pay attention and stop it, it reboots when it wants to. It just rebooted while doing a file transfer unattended. It killed the transfer 50 minutes into it.

When I want to shut down the computer myself, most of the time Outlook prevents closing, but when Windows want to reboot, it does not care which programs I have open. In the middle of anything, it reboots.

How can I change this to make it have my approval before rebooting. If this cannot be done, where do I change the timing?