Peter , I'm not sure what the time frame for getting the BCR2 to a fully charged state with the wall wart would be.
I've never done a charge on a BCR2 outside of the locomotive . I have left the MTH stock battery pack charged on the wall wart charger for a very long time and I have never felt the batteries nor the charger getting hot. When I check the battery pack with my VOM I find it to be well charged. I don't know if there is some safety overload system involved or not.
All my ps2 with BCR2s and my ps3 locomotives gettrack power for at least two or three minutes before I start them up...... Usually I dont get in a hurry and find a couple other things to do before the start up , sometimes for much longer than two or three minutes with no ill effect. ( the " cab chatter " can sometimes be annoying while I'm working on something else though )
My track power is supplied by the Z1000 , TIU , and remote for The DCS full system.
Happy charging Peter.