Seems that how the 3 times per week is implemented will be down to individual units. Some might opt for 3 formal sessions, some might opt for one formal session and two voluntary.
The latter at least has to advantage of flexibility albeit difficult to monitor except on trust. The formal session also offers advantages as the fitness test will include press ups and sit ups. Formal gymwork will ensure that these are improved gradually and avoid the overweight/back-back problems endemic in sudden semi-annual testing.
The '50-minutes' may also be flexible. One unit may opt for a 50 minute sweat session - you need 20 minutes before you enter a weigh loss regime. Another may aim to have PE down time limited to 50 min including travel, changing and showering.
I would almost guess that units without facilities would Swan it
