I missed a coach Cambridge to Stansted today as my train was a couple of minutes late, leaving me 5 minutes to find the coach which I failed to do in time.
Apparently 5 mins is the official connection time, is this reasonable even if it was platform to platform?
Not in my opinion, no - I just posted about that
on a different thread yesterday.
Before the island platform was built, yes, just about (although even then going from the London end of platform 3 to a departure on platform 6, or 4a, could be tight). Now it isn't - going from say the London end of platform 8 to a departure on platform 3 would be difficult to make in 5 minutes even at a brisk walk.
Replacement buses make it even worse. Years ago they'd go from the car park adjacent to platform 6, often with the exit gate there open to assist in making the connection (and making where to go more obvious). Now they go from the bus station, often the far end of the bus station, which is quite a hike from the station entrance, and I don't think I've seen the gate by platform 3 open in some years.
I think it is fair to say that eg. going from the London end of 7/8 to catching a RRB from the far end of the bus station, even if you're 100% sure of where you're going, is basically impossible in 5 minutes unless you have the ability to fly.
All that said there are implications for what are considered valid connections in increasing the minimum connection time, so it wouldn't necessarily be beneficial if this were increased.