Wish there's way to do a Character count on Captions with caption workflow. I'm limiting to a 42 characters per line, and currently using Excel for this task. Character Count Indicator, and Caption Duration (subtitle reading speed - characters per second) are my wish list for the next Caption workflow update!
We would recommend you to submit a feature request for this at our UserVoice page. You may also vote for other ideas that you find interesting. Hope you find it useful. Let us know if you have any questions.