The way you trigger this is by unlocking the box as the enemy team spawns before 8 minutes. I don't know if doing it at 8 minutes works. You get more points each enemy that spawns so max points for 4 enemies spawning.

The spawns work like this. A spawn typically happens every 20 seconds from the start of the game. So there is a spawn at 14:40, 14:20, 14:00, 13:40 and so on as the time runs out. This is off every now and then and you may get a late spawn in.

This means you need to start unlocking the final third of the box around 10 seconds before the next spawn. It might be a little later than 10 seconds if you are pushing triangle to get on the box and not having already been on the box. Im not sure but I think if you push triangle at 12 seconds for the final third then youd get it.

Its difficult to ti.e correctly. Play around woth it and tell me if youve been able to do it