Official comment
Yep - My Core i7 processing a library of 52K songs (MP3s mostly) was over 24hrs to bring it in from 5 to 6, then another 24hrs to addd the new analysis data. So long as you're past the conversion stage, you're able to close and open rekordbox as needed to analyse the tracks. Make sure you've got it set for PERFORMANCE analysis mode so it runs multiple files simultaneously.
