How long do defend quests last?

I played a round of Dominion last night and noticed two quests that came up for our team. One of them was for capturing a point, and the other was for defending another point. Our team wasn't doing too well at capturing the required point so I decided to help out with the defense point. We defended it for a good five minutes or so, repelling several enemy attack waves. Alas, in the end the enemy managed to capture it.

My question is, how long do you need to defend a point in order to complete the actual quest? There doesn't appear to be any kind of explicit indicator for this in the game. Capturing a point is pretty simple, once you capture the point, you complete the quest. But defending something is different, how do you know when you're actually "done" defending? I can't imagine it's indefinitely, because what would be the point of the bonus you would receive for the quest?

Solution 1:

You have one false assumption in your question: what you observed was not two quests, but rather only one.

In other words, the quest was "Capture Point X, while defending point Y from Capture". The quest lasts until one team manages to capture the other, which means, in your case, the 'defend' portion of the quest lasts until your team manages to capture the enemy point in question, rather than a simpler, "defend for X".

You could theoretically have to defend that point for the rest of the game, as long as neither of the two target points changes hands.