I've only just seen this thread and already all the juicy stuff seems to have been deleted!
Can't comment on the specific case, but instead of lining one up in a tightish gap, I've found it often worth waiting a few extra seconds to see just how fast / long the previous lander touches down, ie if it's going to make a particular (or the only!) turn-off. This always was the case if the difference was between a go-around for the next inbound, or saving 2 minutes for a waiting departure, no matter how eager to roll!
Naturally this depends on spacing, wind, aircraft type etc. Friends who fly commercially admit that there is a perceived difference over what's acceptable, depending upon whether you're lining up and ready to expedite, or winding back to minimum approach speed and waiting for a landing clearance.....
As for the Calibrator - ILS's don't actually need any calibration at all. The aircraft is employed to travel round the country providing live TRUCE training for ATC staff....