I'm far from an FT expert nor BAA official. But this question has been raised numerous times since T5 opened and the answer usually is the same--the folks in the know tell us that the complications of T5 mean that it is just not often possible for them to know very far in advance where a plane might be for boarding--which stand, etc.

I welcome others more expert than I to answer this, or whether there might be another better explanation; but this has always been the answer when inquiries were made.

And the reverse can also apply. Yesterday in the T5 Galleries Lounge it said to board now. Went to the C terminal only to find no activity at all. And had a long (almost 30 minutes) in the gate chairs until Fast Track boarding commenced. As the lounge board advises it takes 15 minutes to get to C, it still seemed that board "now" coming 50 minutes prior to the real boarding commencing was a bit odd. (Plane left on the dot on time--so no departure delay involved.)

Had it been the B terminal and that gate near the B lounge, one could have popped upstairs for a cuppa or something, keeping an eye on the gate for activity. But in C..well. There you are when boarding time is in limbo...