Tightening a connector?

60 nanoseconds at the speed of light (299,792,458 m/s) would be nearly 18 metres. Taking into account the relative propagation speed of a signal in a typical coaxial cable at 0.7 they would need to take out 12 metres of cable. A poor connection might introduce resistance and a slow rise time, but if they are basing this measurement on the timing pulse output from a GPS receiver then they deserve the results they got.