Zonky wrote:
Sorry, but what's the point of it? Turning an express train into a
slow stopper for the last couple of miles?

It's no different from WCML trains stopping at Watford Junction. It
relieves the pressure on capacity at Kings Cross St Pancras, though
presumably it will be only some trains that stop at Stratford. (Hmm, wonder
if Freedom Passes wil be accepted for Stratford-St Pancras?)

How long does a "stop" take for the Eurostar?

No longer than for any other long distance express in my experience.
--
Richard J.
(to e-mail me, swap uk and yon in address)