In message , at 14:04:26 on
Sun, 28 Nov 2010, Neil Williams
remarked:
As I think others have posted, the usual convention is that if it's a
timetabled time, it is shown as the time, but if it's real-time it's
shown as a number of minutes.

That's also for signs which show one or the other at different times of
day, or for different buses (depending on how well they are tracking the
buses at the time).

It sounds like the Milton Keynes ones show the time, always. But it's
going to be fairly obvious that it's not showing the timetable because
you can compare it to the timetable you are expecting and it's quite
likely to be a minute or two before or after at random.
--
Roland Perry