How long should it take to encrypt a backup drive using Time Machine?

I recently stopped using time capsule WIFI backups and transferred my old backups to a new Lacie 4 tb USB-connected drive to my Late 2015 27" iMac. macOs 10.15.7. I'm using 2.07 tb out of the available 4.

I did an itinital backup, and things were working well for a day. Then I decided to encrypt that disk. It has been approximately 72 hours and the encryption is only 36% complete. I turned off automatic backups thinking that was slowing things down, but not appreciably. I'm manually backing up once or twice a day, and I can enter Time Machine and the backups are still fine going back a week when I started doing them. Each backup is pretty quickly done. My question is: Is this going on too slowly, and if so, is there a possibility there's a corruption that will only be evident in a week or so when the encryption process finally completes. because that's how long it will take at this rate.