Hi Jason,
The length of time to complete the mp3 mirror files depends on how many '.flac' files there are in your collection.
The B2 will create '.mp3' files at the rate of about 15 tracks per hour, or about 360 tracks per 24 hours.
You can find out how many 'mp3' tracks have been done, using the B2 Remote Control and press the 'Info' button twice. This will display a line: 'x YouTubes yyyy mirrored'
The value 'yyyy' is the number of '.mp3' files that the B2 has created to date.
If you press the 'Info' button twice more, then you should see a line displaying the number of 'flac' files. The difference between this value and the value 'yyyy' is the number of files still to be done.
You can stop the process by pressing and holding the 'Play/Stop' button on the front panel until you see 'Saving' being dipayed on the screen. To prevent the compression from starting again, you will need to change the compression setting from 'flac + mp3' to 'flac'.
Regards,
Peter.