When does a city with 175 points disappear?

shave545

Peltast
Hello!

I don't know whether this question has been asked here before, but I haven't found an answer for it.
I would be curious to know when does exactly a 175 point city disappear and create a colonizable space?
Just for the fact that this morning I tried to colonize some areas like this, but I was late to all of them? How can I get the perfect timing and calculate when these cities disappear?

Thank you for your answers in advance!
 
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