One of Overwatch's many in-game metrics is "Objective Time".
It makes sense when attacking, when you are with the payload or are on a capture point, that I think objective time measures how long you are with the objective, but for defenders, what is defined as 'objective time'? Is it how long you prevent the enemy from touching the objective, like moving the payload, or is it how long you stay alive? I've had times where on defense, I had received some form of Objective Time on the scoreboard despite being nowhere near the objectives at all.
What is objective time, and especially what does it mean in terms of being on defense?