Tim Roll-Pickering wrote:

I think it's two hours which is supposed to cover all journeys on the
system - but does that include the likely waiting time on platforms?
What happens if you touch in at Chesham only to see the train doors
close, and then thanks to delays don't get onto the main part of the
Met for nearly an hour?

It has recently been extended to 2 1/2 hours to allow for the apparent
problems such as you describe.

Paul S