No it isn't, unless you keep a completely unnatural and very strenuous artificial light environment. Not just any light source either. This is worse than people who can't eat most foods and have to have an extremely picky diet, because at least they can do that anywhere and can create a stash of food. To expect this of anyone is ignorant and cruel, IMO.

> Unless you think you'd never resynchronize after moving across the world

The synchronization is to the sun and its light, not to human clocks. That it seems to be the same is because the latter mimic the former, not the other way around. So you can't just use an arbitrary clock, not with any reasonable effort.