Ranks 9-10 do not reduce cooldown as the description indicates. I have it maxxed and the cooldown is still 20 minutes.
http://www.raidloot.com/AA.aspx?name=forceful rejuv Ranks 2-4 and 10 reduce the reuse time of this ability by 3 minutes per rank. Ranks 5-8 by 6 minutes per rank. Rank 9 by 4 minutes. Rank 2: 57 Rank 3: 54 Rank 4: 51 Rank 5: 45 Rank 6: 39 Rank 7: 33 Rank 8: 27 Rank 9: 23 Rank 10: 20