I think there is a more simple way. Periodically check your clock mid game and "ration" off your clock as comparison. If you are playing a 10 min game and are on move 20, then since the average chess game lasts 40 moves, we should have roughly 5 minutes on our clock (half the game and half the time used), or perhaps slightly more in case the game goes past the 40 move average.
Insight on How to Know If You are Playing Too Fast or Too Slow

Very nice , so a good reading is between -10 and +10 , I checked mine was -11.7 for blitz so playing too slow

Sorry, the equation is wrong. Here is the right one.
S = (Tw - Tl) - (Rw - Rl)
S = (8.1 - 1.8) - (53.8 - 63)
S = 15.5
He is playing too fast.

To justify this equation
If you won by resignation, you had probably think much that makes you play too slow but won because you gain huge advantage and because of this he resigned.
If you lose by resignation, the opposite happens.
Won by timeout means you are faster than your opponent
Lose by timeout means the opposite happens.

As per your new equation my result has become -102.1!!!!! which means I am the slowest player on the planet you check for yourself , my wins by timeout 16.9 , losses by time, 73.9, wins by resign 53.8 ,losses by resign 8.7

To justify this equation
If you won by resignation, you had probably think much that makes you play too slow but won because you gain huge advantage and because of this he resigned.
If you lose by resignation, the opposite happens.
Won by timeout means you are faster than your opponent
Lose by timeout means the opposite happens.
Honestly, I don't understand any of this.
If you won by resignation, it is because your opponent resigned. It has absolutely nothing to do with your time management. Similarly, if you lose by resignation, it is because you resigned. By the way, most players should never resign in blitz games.
If you lose by timeout, it tells you that you are probably playing too slow, that is true. But if you win by timeout, that tells you something about your opponent (probabl plays too slow), but nothing about you.

Thanks for informing me. Then we will add another variable. The equation will be.
S = (Tw - Tl) - (Rw - Rl) - (Cw - Cl)
To justify this equation, we will add the following reasons.
If you won by checkmate, you had probably think much that makes you play too slow but won by checkmate.
If you lose by checkmate, the opposite happens.
Then, from the example above.
S = (8.1 - 1.8) - (53.8 - 63) - (35.2 - 33.2)
S = 13.5
He is playing too fast

Now including checkmates my result has become -113.7 !!! Even worse than before man this doesn't seem to make much sense now, perhaps your earlier version of the equation was right

Honestly, I don't understand any of this.
If you won by resignation, it is because your opponent resigned. It has absolutely nothing to do with your time management. Similarly, if you lose by resignation, it is because you resigned. By the way, most players should never resign in blitz games.
If you lose by timeout, it tells you that you are probably playing too slow, that is true. But if you win by timeout, that tells you something about your opponent (probabl plays too slow), but nothing about you.
I agree. But on the larger scheme of things, things that might not seems related are connected to each other because they happen at the same place and time even though they have different reasons. If you won by timeout, it means that you have an ample amount of time to think than your opponent so you can take your time thinking better moves. If you won by resignation, your opponent mostly missed your tactics because he did not take his time calculating moves then he had more time than you. If he uses his time rightly the way you do, he might probably won by timeout. The opposite might be true also.

Now including checkmates my result has become -113.7 !!! Even worse than before man this doesn't seem to make much sense now, perhaps your earlier version of the equation was right
Maybe the second equation is right. I still don't know why checkmates should not be included. Can you think of a reason?

But on the larger scheme of things, things that might not seems related are connected to each other because they happen at the same place and time even though they have different reasons. If you won by timeout, it means that you have an ample amount of time to think than your opponent so you can take your time thinking better moves. If you won by resignation, your opponent mostly missed your tactics because he did not take his time calculating moves then he had more time than you. If he uses his time rightly the way you do, he might probably won by timeout. The opposite might be true also.
I think that you are just wrong. These connections do not exist.
If you win by timeout, you may have a ton of time left, or you may have 0.1 second left. No way to tell.
If you win by resignation, you may have more time than your opponent, or you may have less, there is absolutely no logical reason for any of those to be the case.

Now including checkmates my result has become -113.7 !!! Even worse than before man this doesn't seem to make much sense now, perhaps your earlier version of the equation was right
Yes that is right but I still don't know the best range if you are so fast or slow. 10 is still arbitrary.

Why does winning by checkmate mean you’re playing too slow?
Because most of the time, you are spending your time thinking checkmate patterns.

I think that you are just wrong. These connections do not exist.
If you win by timeout, you may have a ton of time left, or you may have 0.1 second left. No way to tell.
If you win by resignation, you may have more time than your opponent, or you may have less, there is absolutely no logical reason for any of those to be the case.
Yes all of these things are true. This equation is still arbitrary because there are many variables not included and this is not a perfect measure on how we really perform in our games. Besides, if you have a second thought, you might get help from this equation to determine your performance.

All of the things that I wrote here are just pure speculations and cannot be justified or disprove. We had to know by our own selves on how we are performing. If you are lost and you want to know a reason why, you can still consult the equation above but I assure you that this is not a perfect measure of your performance and take it with a grain of salt.
I just notice something on player stats and I also want to know your opinion. Maybe, there is a way to know if you are playing too slow or too fast. And here is what I found.
You can tell if you moving too fast or slow by means of this equation:
S = (Rw - Rl) + (Tw - Tl)
where:
Rw = Wins by Resignation
Rl = Losses by Resignation
Tw = Wins by Timeout
Tl = Losses by Timeout
If S > 10, you are playing too fast
If -10 < S < 10 you are using your time right
If S < -10, you are playing too slow.
In the example above, we can tell how he is managing his time.
S = (53.8 - 63) + (8.1 - 1.8)
S = -2.9
He is using his time right.