Hello,
by default we should not scan Time Machine backups when scanning. We have seen a case where the first read of a file in Time Machine partition took 15 seconds to finish (probably something in Apple's driver, this is not easily detectable), which of course slows down the scan a lot.
Just stop the scan, the detections found should still be in the report. And I suggest turning off "scan Time Machine backup" option of the scan you are starting.
Kind regards,
Ondrej Kolacek