You should have a tactical approach to counter anything efficient in the chain of defense and follow up with a counter attack. If your opponent chooses anything less efficient which is possible in the chain of defense, your counter attack would reach him before your block.
The end result would be the lesser efficient opponent would be in disadvantage and the comprehensive and timing of the disadvantages will determine the outcome of a fight.
In efficient scenarios it should not take more than few splits of a second! So to get to that level you need to devise your training prudently. We do Punching range blocks from various initial body positions assuming it is possible to start a confrontation from this range. Then we go to the longer kicking range and train with devised tactics in that range.
So the human reaction time limit is forgotten in these arts and probably half of the training will never materialize during an efficient attack...But remember that when you start with a projected attack or in sports competition, you have the time to get into a preferred training stance and while you might be projecting your attack and defense capabilities to an experienced opponent, you also get comfortable in the preparation to execute your favorable techniques.
So some tactics are not suitable for some fighting sports as the block or counter are not allowed in a particular sports, and vice versa, some techniques usable in some sports are not suitable for self defense, because they are not giving you the optimal response and counter in all the angles and timing...