Just seen on another forum that members are arranging a Zone 1 (except
Blackfriars) 'Tube challenge' where they aim to visit all stations in
the shortest possible time for a competition between members (not a
world record attempt or anything).

It has been raised that there may be problems with Oyster PAYG and that
users should instead buy a z1-2 Travelcard. What would happen if someone
touched in and didn't touch out again for say 3 hours, even then they
may touch out at a different location? Would there be the £4 minimum
charge or would something else happen?

Cheers