"Timing is the skill of executing a move at the right time. What is the “right time”? It’s the time at which the move can be the most effective.
Some moves work without timing, providing you have a strength advantage or leverage, or both. If your opponent is standing square on his feet, poised and ready with good balance, you may be able to lift him and throw him anyway if you are much stronger. No timing involved. You will however spend a lot of energy, and your chances of getting countered are very high, especially if your opponent is skilled.
Whenever you do a move, you want to think about the right time to do it. Figure out the right timing.
The proper timing requires the following conditions to be true:
1. Your opponent moves into the (weak) position you anticipated, the way you anticipated;
2. You are in the right place to do the technique;
3. Your position allows you to perform the technique; and
4. You know how to perform the technique.
If these 4 conditions above are met, you can execute the technique with good timing.
#4 is your technical skill.
#1-3 have to do with predicting the future: You need to know where your opponent is going to be ahead of time, so you can put yourself in the right spot and position yourself in such a way that when the opponent gets into the weak position, you are ready to attack.
Some people think of timing in terms of fast reaction time: you see a weakness and you attack it right away before your opponent gets a chance to make himself secure.
This is a shortsighted approach and will only work if the opponent remains in a weak position for a long time. It happens, especially in groundwork where people can spend several seconds or even minutes in weak positions because they don’t realize they are exposed. Standing, timing is far more difficult to achieve as people, even beginners, move and constantly shift their balance.
Fast reaction times will only do so much. To have good timing, you need to predict your opponent’s position and movement several seconds in advance."
I agree with all of this, except point 1. I agree that's definitely helpful, but not needed. You have the option of that, or noticing when your opponent has moved to a weak position of which you know a technique. While it's better to set things up, it's important to always pay attention and see if your opponent gives you any extra openings you can use.
Might be nitpicky, but important.
Not nitpicky, but an important distinction per the definition and drills above. I will add that one can be vulnerable to feints (e.g., foot, strikes, etc.). We already agree set ups are better. For more clarity, I will continue the timing definition that includes, "
Causation."
There are ways to predict the future:
1. Direct observation;
2. patterns; and
3. Causation
The same principles apply to grappling. When you see/feel your opponent lifting his back leg, you know that in less than a second, all his weight will be on his front leg. You also know that his back leg will most likely be coming forward and about half a second later his weight will shift onto it.
These are opportunities to apply your techniques with timing. It is however extremely difficult to do on direct observation due to the speed involved. Half a second is very short if you need to position yourself and attack. To have more time to prepare, you can look for patterns in your opponent’s movement. If you can figure out what he is going to do a few seconds ahead of time, it will be much easier to attack with proper timing.
However, your opponent will react to your movement and if you are familiar with Sci-Fi B-movies, you know that your actions can change the future.

If your opponent notices you are getting ready for a technique, he will avoid it, or worse, counter it.
Attacking based on pure observation is hard, you must be fast and your technique must be very good. Fortunately, there is an alternative.
Causation.
You make your opponent behave in the way you need to execute your technique. This is what we usually call a set-up.
The classic example is pushing your opponent. Most opponents will push back. You can prepare yourself to take advantage of that reaction so that when your opponent pushes back, you are ready to throw him forward.
However, not all opponents will react the same way. Some might just step back, or to the side, etc. To increase your success rate, you can try it a few times and observe how the opponent reacts. Once you know what the opponent will do, you can then attack accordingly.
Either way, the window of opportunity is seldom open for very long, so your ability to perform the technique must be very high to take advantage of it.
Timing, attacking at the right time, is the key to effortless technique. It is a major factor in good grappling.