There is no way to tell how long a full scan takes.
There are many variables.
Some are:
- System speed
- Other things running
- File sizes
- Files compressed or not
- Settings for the scan
and many more.
The sparsebundle folder can be very large.
If I understood it correctly, you can remove it without causing any problems.
Perhaps removing it (or at least emptying it) before running the scan is helping.
As I am not a expert on mac's don't take my word for it but do some research I would say, or wait till someone else joins and help you out.