Fishing. Especially bait fishing on the shore of a small, heavily fished lake without any beer or tobacco.
Are there any particular exercises for developing patience?

That could actually work. But there are no lakes nearby where I live. And even if there were the water would be so polluted so as not to have any fish.

In OTB play, I write down my move times. Then when I review the game, I can see that my blunders were a result of spending too little time thinking.

I suggest sitting on your hands after you make a move, and don’t make a move until you’ve briefly analysed several good moves. Hope that helps good luck 🍀

It's more a thing of checking the available threats for you, and those to your adversary. If none at the moment, which pawn/piece arrangements will likely produce threats for one or another. If you can do that in three seconds or less, then good for you.
As for strong players moving instantly, it goes more to them being familiarized with the position on the board, meaning they did that work previously. When not familiar with what's happening, then blunders arise here and there... which is the reason why we take our time: To avoid blundering (at least that often).
So, it's not patience but practicality, in the sense of not wasting our own time by committing fully avoidable mistakes.

I suggest sitting on your hands after you make a move, and don’t make a move until you’ve briefly analysed several good moves. Hope that helps good luck 🍀
That could actually be a good exercise. I'll try it.

It's more a thing of checking the available threats for you, and those to your adversary. If none at the moment, which pawn/piece arrangements will likely produce threats for one or another. If you can do that in three seconds or less, then good for you.
As for strong players moving instantly, it goes more to them being familiarized with the position on the board, meaning they did that work previously. When not familiar with what's happening, then blunders arise here and there... which is the reason why we take our time: To avoid blundering (at least that often).
So, it's not patience but practicality, in the sense of not wasting our own time by committing fully avoidable mistakes.
I've come up with another exercise. I should make sure I count up to 10 moves in n variations and only then make one actual move.

It's not exactly about calculation per se, but detecting the threats for both sides and only then to calculate, as to clarify their strength (can they be neutralized or is a matter of slowing them down by counterattack?). Point being that without making an inventory of the threats for both sides the calculation will likely have holes... and become a waste of time.
Of course, it requires discipline not to play intuitively and fast, but this explains why several players do good in blitz against titled players, but not that good when the titled players have time to think (and punish the lack of work behind their opponents' play).

i agree with that. but is there any concrete way i can delay my moves. like writing down the threats on a piece of paper etc.

Sitting on the hands is actually a good way to avoid playing to fast. As Nicator wrote above, you have to go over the board to see threats, also positional ones. Strong players will not hesitate to sac the quality to put (for example) a knight close to your king. The better you play, the more you see threats.
Another thing: after you found a good move, check it out if there is a better one. For all those things you need time. If would be also useful to stop completely playing blitz and play longer games to get used with longer time controls.

Read the board. Form a plan based on this and then list candidate moves based on this plan. Quick check for any tactics and then make you move. Takes longer than 3 seconds if you are doing it right.
There are lots of books out there that teach you to read a board. Silman's Amatuer's mind is good for this but he also has a ton of articles on here:
https://www.chess.com/article/view/plans-losing-streaks-and-petrosian-speaks

You may be a blitz player by heart, so maybe you can just play quick chess, instead of trying to transition into classical time controls.
But blitz doesn’t allow the player to think long enough to always play a good move. I think a mix of both is good

You may be a blitz player by heart, so maybe you can just play quick chess, instead of trying to transition into classical time controls.
I don't know frankly I've always played blitz because it's much easier to find opponents more quickly in 5 min. If 20min was the most popular time control I would be playing that.
I am used to blitz and I move very (very) quickly. Even when I am playing long games I make a move within 3 seconds when I should take 3 minutes.
Any ideas on how to overcome this habit will be helpful.
Thanks in advance.