Teeteringhead,
In the 1950s, as you say, aircrew on ground tours, had to get in some airborne time - it was applied to ALL aircrew similarly employed. As an Air Siggie at the time, engaged in teaching the signals environment to pilots, I was sent once a year to an active flying station where I sat in Varsity aircraft for bum-numbing hours tootling around the UK with trainee Navs. (Once an hour I would send a Position Report based on application to my Consol chart of data from the Consol beacons.) Being based at Nos. 1 and 4 FTSs I got various amounts of time sitting unproductively in Vampire T11s. There may have been a minimum number of hours required to retain flying pay but I cannot recall there ever being a 'scramble' at the end of the year.