TKD wrote:
I suspect that a tube journey from Cockfosters to Heathrow Airport on
the Piccadilly Line would be very close to 2 hours long in normal
circumstances.

It's 1hr 25mins.

Chesham to Chigwell is 2 hrs 2 mins (with walking speed set to slow).

For these types of journeys, the waiting time is also important. At a
gated station, you touch in, then wait - at somewhere in the far-flung
reaches of the Tube like Amersham, you could potentially wait 20 minutes
for a train (similarly at Baker Street in the other direction).

I found this to be an issue with the allowed out-of-gate interchange
time - when changing from Bakerloo to Chiltern at Marylebone for a train
to Amersham, you might find that you had 30 minutes to wait for your
train, and could potentially fall foul of the system, as you would only
touch in again when your train is ready for boarding.

--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London