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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.