iPad won't auto update because an alarm is set, but there are no alarms set

I've never been able to automatically update my iPad. I get the notification, and leave it plugged in overnight. However, when I wake up, the update has not been installed and I am greeted with the following message:

This update will try again later because there was an alarm set

However, there are no alarms enabled on my iPad.

Edit: I am aware that I can update manually, but I would like to get auto-update working.