Even if the real length of a column is 11, you are not passing from the column of the same type to the column of the same type but with smaller size. So it will be not "metadata-only" operation. Another column will be created instead of your varchar, and this time the column will be fixed-length column.
This means that every row will be touched. If there is not enough space on every page to accomodate new column, new page will be allocated. This means you'll get a lot of
forwarding records in case of a heap and a lot of
page splits in case of clustered table.
In every case your table size will grow until the next table rebuild, and it will be made in one transaction that means huge log writing and much time engaged.
If you absolutely need to change this column type, it may be more convenient new column of correct type creation an its updating in a small batches, then dropping old column, or maybe new table creation will be less resource intensive because you can split loading data into batches (but it will require additional space equal to your table size).
You can also consider adding
computed column as a cast of existing column and creating index on it.