Takes less than a minute for me. I have about 30 or less RBN songs and I have downloaded lots of track previews. Also, no creator account.
Perhaps it is linked to a specific track, much like the Apples Energy loop bug?
I don't remember having the problem when RBN first came out so it very well could be associated with number of songs one has purchased from said network. Would have to know how many songs from RBN some of the other folk that have the long loop have purchased.