Why? If it takes 2 minutes it's because it's unclear, so give up after 20-30 and let the refs decision stand.
If it's something as clear cut as whether someone is half a yard onside or offside when they score a goal, it will take 10 seconds and it'll add zero time because players spend 30 seconds running about hugging each other after a goal. For more debateable offsides, it's normally clear 90% of the time if your aim is to give the benefit of the doubt to the forward.
How many times in a game is an offside goal scored, an onside goal incorrectly ruled offside (and as I said, these two things are likely to add zero time anyway), a questionable penalty is given, a red card tackle goes unpunished or a red card is incorrectly given? In your average game I'd say there were probably 2 of these events.
Do you remember all the fucking about that used to happen when a goal was scored where the ball crossed the line by 1 inch? Both sides convinced it was / wasn't a goal. Now that everyone knows that the ref is 100% right because of goal line technology, there is no issue and nobody complains. If it's decided that the video referee is the ultimate authority and their decision always stands then there's nothing to whine about, or at least no reason to do your moaning at the referee. All the video referee is doing is making the same decision again but with more evidence.