There isn’t one.
When you publish on Medium, Medium will be distributing your content to many, many other readers. How do they choose who to distribute your writing to? By using several factors, such as what topic you wrote the story in, whether the person follows you, whether it’s in a publication that person follows, and whether the story has been curated in a certain topic.
Medium has readers from all over the world, in every time zone. They send out daily, weekly, and monthly email digests to people at all different times. They regularly update and personalize every reader’s homepage to make it current and relevant to that reader.
All of these factors mean that there is no one single best time to post a blog or story on Medium.
From a personal perspective, I’ve found that certain times mean the initial growth will be slower. For example, if I publish after 8 pm GMT, I can expect not many views that first day. But I can expect it to catch up when it’s shown around the next day.
Medium themselves have written about this, and after a lot of number crunching, they found there wasn’t a best time to publish on Medium. A lot of other factors contributed – the length of the piece, how long the author spent editing before publishing, number of followers – but in the end, the conclusion was that there was no best time to publish on Medium.
What I love about Medium is that it takes all the guesswork out of writing. You don’t need to do any fancy formatting, you don’t need to do a whole lot of SEO optimization, your stories will be distributed beyond just your followers without you lifting a finger.
You can’t game the system. All you can do is write well, frequently.