I think it’s cool for you to have work hours. Sellers should add their work hours if they have them and would find them useful in managing buyers and workflow. It adds another layer of professionalism to your work and sets a buyer’s expectations as to when they may hear back from you. Personally, I don’t have any on my gigs since when I work depends on the week.
Some say that it hurts your gigs to turn Out of Office on often, but I think the evidence is more empirical than anything and varied from person to person. For example, I don’t see a change in order volume after coming from a break (after all, I just did for over a week because of Thanksgiving and things are back to the way they were).
I agree with benedictrm in that some people take the info as your imposing rules on them that Fiverr doesn’t technically support, but, like him, I agree the Out of Office feature is there for a reason and think it’s smart to use it more liberally. I’ve only seen one seller post working hours, but maybe more people should do it. If we normalize such a thing, that could be good (nice topic btw).