A day on Avenir is 25 hours, based on the human Circadian rhythm. A day on Eclectia varies between 20 and 30 hours due to the planet's wobble.
This wobble also creates the speedy changes in season. Every five days there is a "winter" and every five days there is a "summer" in between. Each brings extremes of cold and heat, and short/long days. This is called a fiveday and much like on Earth, it begins in the Northern winter and in the South's summer.
Six fivedays make a month, so thirty days. Their names are: Celeste, Dax, Isadek, Terra, Alumnus, Railway, Cathar, Benzine, Illecof, Tower, Macbane, Lantana, Aquarium, Pimpernel and Turnpike. The names originate partly from the Founders' own names and partly from Earth terminology fallen into disuse in this new world. So people might talk about the fourth fiveday of the month like we talk about the third week of the month, as well as specifying dates such as the 29th of Celeste. The year is designated A.F. or After Founding and the current timeframe is 179 A.F., flashbacks excepted.
That gives us 450 days, but the yearly orbit of Eclectia is 454 days. The final four days are the Festival of Founding, something like our New Year. Anyone want to take a stab at how it's celebrated? Customs may vary between settlements, of course, and there may be some shreds of Christmas left over in it.
Okay. So what does it mean when Ave is 14 Foundings old? That's a good bit more than 14 Earth years, because an Avenir year is 3 months longer than ours. Let's do the maths...to make it simple let's assume an equal month length.
14 Foundings x 15 months = 210 months. Divide that by 12 and you have your Earth years: 17 and a half.
It works the same the other way, of course. If you want to say "five years ago" in Earth terms, that is 60 months = 4 Avenir Foundings.
Clear as mud?