I think that is for every job the same. You cant do max duration Guard anymore, or the coordinated burst/cc will kill you right after, as they will definetly press their skills already at 1s remaining of your Guard. So canceling Guard at 3-4s may be better. But that also means that the enemy team will more often than not just burst into your Guard, as they expect that to happen anyway. Which is bad, because bursting into Guard should punish you, but it is actually not that bad. Another way to reward bad players for pressing their skills and punish good players for pressing Guard at the right moment.