It is actually possible to search by bpm or length.
- Search for BPM: http://audiojungle.net/browse/attributes/bpm/ (type the bpm you want here)
- Search for length: http://audiojungle.net/browse/attributes/length/ (type the length you want here)
That’s kind of a roundabout, band-aid solution, but will do for now I suppose. The major detriment to that method is you can’t then narrow it down by category or any other attribute also.