I never finished even played Days and BBS is my favorite KH game. Although I did read up on the story of Days, so... I guess if you still plan on playing it, maybe you should finish it. But if you really can't wait, go ahead and play BBS now and go back to Days later, maybe before you get the secret ending of BBS.
--
~Halo Give into the Night.
http://i10.photobucket.com/albums/a125/ShadowHalo/haloshadow1.gif