On Fri, 21 May 2010 00:38:16 -0700 (PDT), Paul Corfield
wrote:

No firm dates yet but Jan or Feb 2011 are the dates I've seen
suggested in various TfL reports. Oddly the updated London Overground
pages on the TfL website say "by May 2011" which is quite a difference
in timing but aligns with the national timetable date change.

Weren't they been publicising the current opening as May 2010, then
opened the preview service to the public on a limited timetable.
Following the same procedure to H&L would be logical - run a limited
service of through trains (e.g. finishing at 2000) then open fully
under the May timetable.