Unless you are really insecure about your proficiency in any work-related tasks, I would strongly suggest against doing anything work related in your spare time

Unless you are really insecure about your proficiency in any work-related tasks, I would strongly suggest against doing anything work related in your spare time. It would only dilute your salary (now you're working 1-2 extra hours every day for the same pay), and while it might provide you a slight productivity boost (unless you burn out), if you ever were to need those hours back it would be difficult to explain the lower performance at work. If you want to improve your skills, I would suggest reading, taking a course, working on your own projects, anything by spending time on work-related stuff. Unless you're the founder, in which case what are you doing not working 24/7.