To me it seems that standardized business hours arise from cooperation in the work place, which increased exponentially with the industrial revolution. Capitalist, socialist, whatever, if you have people cooperating in factories (e.g.) then they have to be there at the same time. So "bedtime abolition" seems utopian because it is the practical consequence of a cooperative productive process, and it can't be abolished without abolishing the actual basis, cooperative labor, or more specifically the necessity of simultaneous work. Our production would have to change such that work is parceled out in time-independent units, which is possible for a lot of industries, but by a structural change and not by decree. Software development is cooperative but does not typically require that developers cooperate in real time, for example.

And of course, the above is made all the more severe by the actual duration of the working day. If people only had to work 4 hours per day, then it would be far easier to handle standard business hours of 10a-2p for example, even if they technically are not flexible hours.