It can take up to 10 hours, over 30 passes on low end processors. I suggest a disk cleanup before starting a defrag, and also consider if it is really necessary.

Why does Windows 10 defrag take so long?

The larger the hard drive, the longer it will take; the more files stored, the more time computer will require to defrag all of them. The time varies computer to computer as each one has its own unique case. The time can range from several minutes to several hours to finish.

How long does it take to defrag a hard drive Windows 10?

Disk Defragmenter might take from several minutes to a few hours to finish, depending on the size and degree of fragmentation of your hard disk. You can still use your computer during the defragmentation process.