Well looks like your internal memory had some bad blocks. Kind of a good sign that you have got out of the endless reboot loop you had.
I honestly don't know how long it takes. Going off the other thread unfortunately there isn't any mention of time.
Not sure if you read further but
https://www.mobileread.com/forums/showthread.php?t=79036 is the actual thread where the Cleaning thing actually came from. Looks like it reformats the firmware partition.