You should remove the brackets as they are not part of the ISBN numbers - LibraryThing introduces them to save the leading zero, which gets dropped in an Excel format. So what you have to do is remove the brackets while retaining the zeros. This isn't a problem if your ISBN numbers are the 13 digit ones as they all start with 978 but if your numbers are the 10 digit ISBN with leading zeros then this is what you need to do.
The easiest way to get rid of the brackets and keep the leading zeros is to copy the column into Notepad, which is a text file, then remove the brackets by clicking Edit and replace. CTRL H does the same procedure. Once the brackets are removed you can copy the column into our Import Books list. The X at the end of some numbers is important as the last digit is a balancing number and is required for the ISBN to be recognized.
You gave us a good laugh with the half-day idea when you have your own business. It's more like a day and a half fitted into a day. And by the way, I'm on Eastern time so it's now 11:55pm on Sunday night!