I contacted Yakup Yılmaz (Hippy Chick opposite Mulberry Tree) on your behalf and here is his reply.
A POA is indefinite unless it states otherwise. For example it could say 'for three months' or until the job is done, or until September 2013 etc.
Whatever the POA states is the 'power' - this is the only 'power' so if for example you give someone a POA to buy a house, that is all they can do - buy it.
A POA can be given for almost anything. You have to be very clear about what you want done and that is the ONLY thing (or things) that can be done.
If you want to revoke an indefinite power then you will have to go back to the Noter and pay to revoke it and obviously only the person who gave the power in the first place is able to revoke it.
Hope that helps, Yakup's number is 0539 835 19 22 if you want more advice or help.
PS: I posted because Lynda (Yakup's wife) who is/was member of CBF and would have posted but has new email and needs to rejoin and that can take a while to sort out.