I quoted the Journey Planner in asking TfL how the 70 minute peak one
zone maximum journey time was consistent with a customer just missing
the 6.12 from Hackney Wick to Kew Gardens and then taking 84 minutes if
trains run to timetable.

The following is extracted from their reply:

We are, however, aware that there have been isolated cases of customers
finding that they have insufficient time to make long journeys within
zones 1, 2, 1-2, or 2-3.

With this in mind, we have agreed with ATOC that with effect from 2
January 2010 all such journeys will be given Maximum Journey Times, as
though they were 3-zone journeys under the current formula.

Mostly, this adds a further 20 minutes to the time limits for the
journeys in question, during the daytime Monday to Friday. We will be
monitoring the effects of these changes to see if there is still a
problem and it will remain our intention that all legitimate journeys
be given sufficient time.

There was no definition of "legitimate journeys".
--
Walter Briscoe