That's a terrible speed to get points of sequential keys, on a CPU. A good implementation can reach at least 20 million pubKeys / second, on a single thread, on a modest CPU.

its only for to show and learn how the process is done using one thread.
feel free to optimize but its impossible to gain speed with python.
using opencl makes no difference.
that is why to use C..

You wanted something new, I guess, buddy.

1BY8GQbnueykaHFzbhAFTmJwzn1k63uhSB
Hex: 6D56D89328480D4AA

1BY8GQbnueyjTRBwVf4aTYocU2TmFzuhMH
Hex: 59CECCF4F9369CB79

Is that enough for now? (Just kidding.)

Excuse me, let me add these too.

1BY8GQbnueUAXpFh7rEp1QfWRQXdbPBgXQ
Hex: 6CD053767784C37F6

1BY8GQbnueUMG1vCafLpYrP8dqevBV29DZ
Hex: 67ACAA2072F0B8323

I guess it's still mostly speculation of what exactly has happened to puzzle 66.
But in short, let's assume you got really really lucky, and manage to find the private key of puzzle 67, convert the hex private key to wif, login via Electron and start a spending transaction.
As soon as there is a confirmation on the blockchain, the corresponding public key of said wallet is exposed to the public and it's not really hard to write a bot which checks the latest transaction history from any wallet.
That means, if some bot manages to get the public key in time, bruteforcing the private key via bsgs or kangaroo algorithm is not very hard and on any modern gpu would not take longer than a couple of seconds to minutes.
So any stealer can then replace your transaction with higher sats which means the blockchain will prioritize those transactions and you receive nothing.

So to answer your question of "For how long a transaction can be blocked by the processing party":
Just imagine 100 bots attempting to replace the transaction with a slightly higher fee. The will continue so unless no money is to be made. Remember, only the transaction with the highest fee will be processed.

To answer your question of which puzzles are "safe": Any puzzle with high enough entropy which cannot be solved via bsgs/pollard rho/pollard kangaroo within 10 minutes is a safe bet.
However, keep in mind that each time a puzzle is solved, the next one essentially doubles in difficulty, that's why it currently makes little sense to attempt to solve puzzle 68, 69, 70, etc. or 160 via kangaroo.
Stick with either puzzle 67 (normal bruteforcing) or puzzle 135 (kangaroo, not BSGS because BSGS is useless here).

What to really do if you manage to solve low-entropy puzzles
Again, highly speculative but as far as timing goes right - each block is mined approx. every 10 minutes. So if you get your timing right, you should be able to do the spending transaction and the next block is mined within the next seconds which should in theory increase your odds of claiming the reward.
Apart from that, I would likely try to get my timing right and combine it with Mara's slipstream, which I personally have never used, but will when I manage to find some private keys.

In any case, document anything carefully with evidence that YOU found the private key of said wallet which could be viewed at later on if anything goes wrong.

Best regards