No, as long as there is a couple of hours of unscheduled time for the reboot to happen. If you are concerned about when the update occurs a reboot can always be forced when the status is pending restart. (either through the menus or just cycle the power).
Getting the update happens during the scheduled connection the update is download along with the program data and does not interrupt recordings. You can check the status in Settings -> Network -> Connect.
VicW, Ex-Comcast customer ... And loving it!.