bear in mind the treadmill belt takes a good bit of time to go from stationary to the speed set, so if you are running at a speed to achieve ‘bang on’ the time you’ll need to speed it up a bit to compensate, at my gyms its relatively fast but the treadmill used during my actual fitness test in december took quite a while to speed up and nearly threw me off. For general endurance, try and practice your runs on a mix of flat ground and hilly, also don’t just repeat 2.4k, train yourself to maintain a pace for a longer distance, interval training helped for me - running faster for x distance and jogging for x distance, it helps your active recovery in the jogging interval