I showed before that there is a relationship between the succession of the day of the week and the order of the spheres in the geocentric model of the world. If you know the order of the days of the week and the planet associated to each day, you can find back the order of the planetary spheres easily. Just start with Monday and name every other day. That gives us the sequence Monday, Wednesday, Friday, Sunday, Tuesday, Thursday, Saturday. If you replace the name of the day by the name of the planet associated to that day, you find the sequence of the planetary spheres starting from the sphere closer to Earth: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn.
But where this relationship comes from? Which sequence came first, the day of the week or the planetary sphere order? The answer to those two questions is based on the notion of planetary hours.
The notion of hours we use today is somewhat different than it was before. Originally like today, the day was divided into 24 hours, but there was exactly 12 hours in the day and 12 hours in the night. A daytime hour duration was one twelfth of the time measured between sunset and sundown. And a nighttime hour duration was one twelfth of the time measured between sundown and sunset. So, except at the equinox, a daytime hour duration would not be equal to a nighttime hour duration.
Hours were associated to planets using the sequence of the planetary spheres from the farthest to the closest to Earth. This means that if one hour is dedicated to Saturn, the next one will be dedicated to Jupiter. This is a cycle of 7 hours, a new cycle starts again after an hour dedicated to the Moon, starting anew with an hour dedicated to Saturn. Because there is 7 days of 24 hours in a week, there will be 24 cycles of 7 planetary hours in a week.
The relationship between planetary hours and planetary day is based on the planet associated to the first hour after sunset. On a Saturday, the first hour after sunset is dedicated to Saturn. As the remainder of 24 divided by 7 is 3, the planet associated to the first hour of the following day will be 3 spheres closer to Earth, which will be Sun. Hence Sunday follows Saturday. Three spheres down after Sun is the sphere of the Moon, hence Monday follows Sunday.
So we can see that the order of days in a week is related to the order of the planetary spheres through the concept of planetary hours. But which came first? We only see that we could get the planetary spheres order from the sequence of the day of the week and vice versa.
Because the planetary spheres sequence is a model of the world based on interpretation of actual observation, my assumption is that it came first and the order of the day of the week came with the idea of dedicating hours and days to specific planets following the system I just described.