Alternating between counter time and the fridge will speed up the process without over warming. If it is in cryo-vac, I would leave it sealed.
The bucket and/or bathtub soak works. For fastest thaw, put cyro-vaced brisket in a 5 gallon bucket, put the end of a hose inside the bucket, going to the bottem, and run tap water slowly and conteniously, allowing it to overflow the top. Needless to say, bucket need to be positioned where run-off will not be a problem. A couple of hours of this should get it thawed enough so you can finish in the fridge.