We've been asked the question from the title repeatedly. TLDR: it doesn't matter that much.
Let's take each platform for which this question has been asked:
Our working schedule was set up on purpose so that we are active during the time when US and EU hours overlap. That's the highest traffic period for this social media platform. For this reason, worry not, and do ops during our working schedule. You'll have optimized the time variable enough. Of more importance would be for your post to have some actual quality behind it so that it stays up in the hot tab of the subreddit for at least 12 hours.
But maybe you're targeting a non-standard group of people. Then you can use this online tool to find out when it's the best time to post: https://www.redditlater.com/analysis. It uses the timezone reported by your browser. Consider submitting a bit before the recommended time. Or, if you're hiring us to do the posts for you, consider letting us choose the best times, depending on the networks and the post locations. Just specify at checkout that we have free rein with the scheduling. Or don't write anything because that's what we do by default!
Anytime after the first 90 minutes of our working schedule.
If you want to understand better the demographics of this platform, use this: https://www.similarweb.com/website/news.ycombinator.com/#overview. It's basically English-speaking nerds.
Their homepage is based on a 24-hour cycle. This means that the new products hit the homepage at 12:01 am PST. Schedule the post to launch at that time because you'll have a full day to get your desired number of upvotes. You'll have an easier time competing for the top 10 of the week.
If you want to be picky about the day as well, you can use a tool like https://whentolaunch.app to choose the best time. But do realize that if you choose Tuesday, you might end up competing with products from some established brands.