Basically, it's your choice. But stop over-thinking it.
And I don't have experience making estimate tax payments previously, and don't want to introduce a new process (and deadlines) if I don't have to
http://www.irs.gov/payments for the quarter you realize the gain, and you're done. You don't even have to wait for that quarter to get here either. So if you want to pay taxes for the 2021 fourth quarter, today, knock yourself out.
