Today's world is highly interconnected and one person can speak with another person with no practical time lag.
But as the Roman Empire showed there is a breaking point. If it takes too much time for orders to arrive from the capital to the frontier, the country cannot sustain itself.
If we expect to conquer the space, we should expect the same problem to crop up again.
So what could be the maximum time for a communication to arrive from the center to the outreaches, so that the state can continue to function?
P.S. I take it that there should be a modifier, where a dictatorship would allow a larger time interval then a democracy.
I am basing this question on my understanding of the reason why the Roman Empire broke into 2 and/or 4 parts. To allow the ruler to govern effectively.
In an ideal world even communism would work. But I am not asking about an ideal world. So the time difference is important for feedback, in case the government has to decide on an issue - be it an invasion, plague, famine...
An issue becomes visible in a representative democracy, take the US presidential election, I think that the place removed by 3 months, could for all practical purposes not vote.
My point about democracy - dictatorship is that a single person can make an instant decision, while several people first have find consensus.