This suggestion worked for me!
My update was about 15% done with step 1 after 2.5 hours. I did this force reboot using the remote, then turned off sleep timer for good measure, then ran the update again from Settings. It was done in ten minutes.
Read on Apple's Support Forums to do this and it worked for me:
Hold down the Menu and Down Arrow button on your remote until the Apple TV reboots. It's light will flash rapidly while it does so. It should come back up normally. Do the update again and it'll finish Step 1 much faster.
My update was about 15% done with step 1 after 2.5 hours. I did this force reboot using the remote, then turned off sleep timer for good measure, then ran the update again from Settings. It was done in ten minutes.