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By post he means tweet, right? Google says average tweet length is only around 30 characters and average word length around 5 characters. So let's say it's 8 words with abbreviation which would take 2 seconds to read. If it's 4 seconds per tweet with scrolling then you can now only spend under an hour on Twitter without paying. Good on him for fighting against social media addiction I guess.
I got rate limited in 25 minutes by refreshing my Following feed and reading about people getting rate limited. I don't think it counts 600 unique tweets since I definitely reloaded the same tweets multiple times.
It's basically everything. Tweets, quoted tweets, replies, and even ads all count against the limit. I've seen people saying they hit the limit in under 10 minutes of scrolling. One person said they only managed to post two tweets before being limited.
And from what I understand spam bots are mostly unaffected since they're already rate limited for reads (but not posts).
Dude is using 100% of his brain to find the best way to cut ad revenue.