Reflecting a bit, I really see not plausible justification why say one account should be let to be logged in for more than 3 hours/day (say specially during workweek). Even if you really have no job, at that point I don't think it's adding to your wellbeing.
I myself really enjoyed a game (Tibia, very popular here in Brazil) during my childhood, and, living in a large metropolis (and at the time quite violent too) and with limited opportunities for play, it was a saving grace in some ways. It really served as a playground analogue to the real world, where I could talk to people from other cultures all over the world, practice a foreign language (english), practice commerce, planning, and lots of really nice things I think it's fair to say. I think excesses of gaming were already in common consciousness at the time, and the occasional warning from my parents (in no way prohibitive) was a great reminder -- me and my older brother did check whether we were getting something good out of the experience. Specially as the dial-up internet cost was very large! (later replaced by broadband to the relief of my father). I'm also glad it didn't overwhelm my childhood.
That game has since added soft limits (already in 2006 according to the wiki), which I think are better than nothing, but probably there should be some hard limits as well (even if you're really conservative about limits... surely at least something like 8 hours a day could be universally agreed upon).
There are valid objections to those kinds of limits because there are all sorts of exceptions: bedridden people that need an activity, people that just use the game as a chatroom (quite common) to keep in touch with friends, etc.. I think those people can find other activities and other media to fill their time and chat.
It's also probably unlikely that those limits are going to be voluntarily enforced by all companies. I think regulation in this area is important -- in a way, those limits are actually good for the medium: they allow a minimally healthy baseline to exist and the market not be dominated by the worst, most damaging grindfests. But also probably just regulation has limits, and it's important for individual/collective conscience, education and cultural awareness to exist, so people pay attention that each activity is adding, to their lives, being meaningful (this includes social media usage, all sorts of games, etc. -- but could apply to doing anything too much like watching TV or talking to friends even). Boredom is the instinctive response that encourages taking other activities, but unfortunately adversarial design and dark patterns (and even just too captivating activities) have found ways to override this response simply to generate profit.
Moreover, as a game designer, we should be really be thinking about bringing worthwhile experiences into this world, things that teach (in all sorts of ways), move, challenge, captivate, inspire and connect us. Here's a heuristic I like: take your favorite memories and feelings and try to replicate, extend and generalize them in various ways for others.