Please follow the steps below to troubleshoot the reason that causes this issue:
1. Normally the deep scan can be completed in around 10 to 12 hours for a 1-TB healthy hard drive in general conditions. It is normal if your scanning time is in this time range. Please wait patiently and do not stop the scan in the middle of the process.
2. If the scan time is longer than the normal time, please check if the hard drive is disconnected from the computer, especially for external ones. Please change a new cable to do the recovery again if disconnected.
3. If the scan time is longer than the normal time, it is also suggested that you pause the scan and then recover the files that have been found already to your other drive and check if they are what you need.
4. Your hard drive contains serious physical errors (such as bad sectors, and bad tracks). Please use a professional tool such as HDTune to diagnose your hard drive. If the diagnosis shows physical error, you may need assistance from a local data recovery lab.