I don't know what you guys will guys will say after asking this but yes it is true that till now I don't understand this features what you are seeing on the screenshot.
Does it shows the only time when I make posts or anything other to means? Because I am seeing that most posts of mine in 6 pm to 8 pm when I sit for the forum activity in mostly.
Lols, I believe that by now, you should already have gotten a good response to your question, but just to add to what most users must have said.
What you are seeing there is a graph 📊 measuring your posting style and the time you made the most posts in every 24 hours.
Look at the beginning of the graph, the times starts from 12 am (the very beginning of a new day), and look the end of the graph, it ends at 11 pm (the last hour of the day before we enter a new day).
So in-between this hours, the graph is there to indicate the time of the day you made the most posts, it's as simply as this.