That's assuming a lot of things about the present level of productivity of everyone working. Also, your number sounds like "household income" and I'm making my assumptions based on GDP per capita[0].
Generally though, yes, I'd assume most people would end up working ~20 hours a week. I'd assume most employers would prefer this, and would also optimize the use of their employees' time.
I think your understanding of Soviet economic policy is probably a bit naive, but for a high level overview of my philosophy, I'd recommend Russell's In Praise of Idleness[1].
[0] https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nomi...