In a lot of these cases, it's fairly irrelevant. Anything past Mars, the Sun is going to be so weak that day and night cycles are based off of artificial lighting. So they can choose whatever standard for time they want. For all of your cylindrical habitats and toruses, some part of the habitat is ALWAYS in day, so again, choose a standardized 'time zone' and be done with it. Mercury the days are a year long, so not a concern there. Around the sun the day is... well, all the time. So again, no concern. Venus the habitats move, so it's whatever they want. Lunar days are extremely long, so they'll want to stick to an artificial clock. Really, the only people who are going to have their own clock is the Barsoomians. The Martian day is something like 23 hours. Given that Mars is sort of the NYC of EP, I'm sure there was some debate about whether they stick to the old Earth calendar and times, just as a standard meter, or if they switch over to the Martian one, so someone is at least using that calendar. I don't know who won on the hourly clock, but it seems clear we use the standard Terran calendar still. For simplicity, I'd argue they still all use the Terran clock as well. Some habitats are adjusted to it (and have 24-hour days that start at 6am and end at 6pm), some are not. The relevancy of the 'universal clock' depends on local standards. Seems simplest and most logical.