Would an employer allow you to take an online graduate school class, unrelated to your job, in the middle of the work day?

[Gravda]

I like to continue education doing grad school part-time online, while working full time. However the degree I may want to get may not be related to the exact job I would be working. Would employers generally have any problem with you taking an online graduate class that you attend via video chat let's say for 1 hour 2 or 3 days a week in the middle of the work day? Can they prevent you from doing that? Is that really their concerns/do you really need to communicate if you're doing that? Obviously you can be willing to work later to compensate for the time spent not working.

This could continue on it definitely for many years. The plan wouldn't be to go to grad school full time within a short time frame. My desires to work and to remain loyal to an employer but I just want to continue my knowledge and education in a particular field of study beyond what I can learn on the undergraduate level.