Wondering when your followers are online the most? Just head to the Reach section, where you'll find the Followers online chart:
Using data from the last 30 days, here you can see hourly data on when your followers are online. Just hover over the gradated circles to see how many followers are online at any given time! The more saturated/the bigger of the circle, the more they are online.
You'll also find this data on the Scheduler - just be sure to select the "Followers online" filter, and the times when your followers are online the most will then show on the calendar: