next time you can head to \Windows\System32\Tasks\Microsoft\Windows\UpdateOrchestrator and rename all the files* containing reboot in their name, or, move them to a backup folder and then create two new folders with exact the same name as the files and set their properties to read-only, so windows can't recreate the original files. And you're done. No more reboots except you want to. My actual uptime: 52:16:07:09 (d:h:m:s) -> Thank me later ;)

*(as I remember there are two files, Reboot_AC and Reboot_Battery)