IIRC, I recall that the working month, for establishment calculations, was around 117 hours. The extra working hours, around 40 hours were 'available ' for other duties such as orderly duties, sick parade, secondary duties, leave and so on. As leave took about 180 hours out of the year or 15 hrs/month that 40 was nearer 25 flex.
With full manning and cold war peacetime, pre-taceval, it was
probably not unrealistic.
However how many people ever reclaimed time while sick on leave for extra leave as you were entitled?