In message , at 17:36:24 on
Mon, 15 Mar 2010, Graham Harrison
remarked:
If you both find somewhere to stop/sit as soon as you exit customs and
immigration my best estimate is that by the time the T4 person has
found the train, bought a ticket (to Russell Sq) and travelled to T123
the T3 person will have walked from T3 to the underground, bought a
ticket (to Russell Sq) and got down onto the platform. Yes, it is
further from T3 to the underground than from T4 to it's platform but
there's the extra travel time from T4 to T123. In the end the total
time isn't that different. In any case, if the agreement is that the
person from T4 will get out at T123 then if the time isn't identical
they can hang around on the platform for a few minutes.

But they are arriving an hour apart.

So one of them will need to kill time at their terminal, before catching
the train. They should "synchronise watches" by phone when above ground
at their separate terminals, then arrange to meet on the T123 platform
about ten minutes later.
--
Roland Perry