Imagine billions of years have been passed and the Sun has been so big that the Earth is completely swallowed by it. Now the habitable zone reaches Europa, one of the moons of Jupiter.
Let's assume Jupiter completes its orbit around the Sun just like today (e.g. every 4333 Earth days) and Europa also completes its orbit around Jupiter every 3.5 Earth days (just like today).
The orbit of Europa around Jupiter is too short to consider it a year for people living there. So we consider the orbit of Jupiter around the Sun a year.
When Jupiter completes its orbit, Europa has orbited around Jupiter 1238 times. Since the moon is tidally locked to the parent planet, Europa also has rotated 1238 times on its own axis; thus each year has 1238 days for people living on Europa.
Let's assume Europa will have four seasons just like the Earth. Also, let's assume that the frequent total solar eclipses by Jupiter doesn't affect the lives of people living on the moon.
Which will be the best choice for the length of months in Europa so that all 1238 days be in 12 months?