Platforms 21 and 22 at Waterloo

You've got signs up at Waterloo asking commuters to leave enough time to catch their trains from these platforms. That's going to be a bit difficult given SWR's apparently ineradicable habit of a) announcing trains at the last possible moment and b) changing platforms without notice. Five minutes from concourse to the end of a 10 coach train is pushing it for me, and I'm relatively nimble and healthy.