There are thousands of tools for social media, and only a few dozen that strike me as useful. One of those is Tweriod, which analyzes your Twitter account, including when followers are most likely to interact with you, and thus when you should post. Best of all, it will auto-populate your account at Buffer, building the schedule for each of your accounts accordingly.
Click to download a 9-page PDF of the data from my account to illustrate what you'll see.