The 1950s economy was the result of:

1. The New Deal
2. A world war which destroyed the infrastructure of every developed economy except for the US.

The New Deal was only possible because of the Great Depression. Only that level of chaos was enough so that left-wing politicians could push through radical reforms that moved power from the elite to the workers. The reforms of the New Deal remained in place after the war, at least for a while.

The second world war saw the destruction of the industrial capacity of the UK, Germany, France and the USSR. Meanwhile the only attack on the US was an attack on military targets at a Navy base in a distant territory.

So, if you want an economy similar to the 1950s, arrange for a world war which somehow leaves the US unscathed but destroys every other similarly developed economy, then arrange for a great depression which destroys the economy to such an extent that radical reforms can be enacted to hand power to the average worker.

Yes, of course nothing bad would happen if we switched to a 20 hour work week. But, the people with the power aren't going to just allow that to happen. The 40 hour work week only happened with a massive series of strikes that were brutally put down by the cops. The change to a 20 hour week isn't just going to happen because some workers think it would be cool.