Hi, I recently heard that from the moment of touching in, I have 2
hours to touch out, otherwise I will pay the penalty for not touching
out. Is that true?

If it is, then it adds a nice feature to travelling to DLR and other
stations without the barriers. I can just go to Canary Wharf shopping
centre, buy some stuff, and go back, paying just 1 quid (i live in
Z2). Is there anything that can go wrong in this method? Any exception
from entering and exiting at the same station etc.?

And last question - is there any website I can check what exact fare
would I be charged when travelling between two stations? On some
journeys there is a choice of going through Z1 or not, and I would
like to know which of these applies on the particular journey.