I personally operate with 1 Riis year is ~11 Earth years, and a Riis day is 27 hours with a longer daylight period due to their 2 suns.
Seasons
(Some of these might not be "seasons" for us, but eliksni also have very huge trade cultures in my headcanons. Some of these names use parts of @abidethetempest's conlang, but others are my own "eliksni sounding" words)
Durrdra: Rough equivalent of winter -- incredibly cold in some places, with lots of water freezing over.
Urthrys: Period when Riis thaws out and one of the shortest seasons. Used as a period of preparation for hunts and harvests. Eliksni often (and instinctually) find life partners or have hatchlings during this time.
Chihrr: Bugs come out in droves during this season and are hunted and harvest for food, or caught and bred as pets.
Shiivath: The hottest season on Riis, an equivalent of summer. A lot of schooling happens around now within Houses.
Viideks: A (typically sudden) rainy and flood season that swamps much of the planet thanks to the prior heat waves.
Liismek: "Frog" breeding season and when tadpoles are gathered and harvested. Also when weaker crops are planted to avoid flood damage.
Kicheth: Similar to spring; usually a time when more mammal-adjacent creatures have their offspring, and is another instance of insect activity.
Taneth: very long farming-into-harvest season. A very busy time of the year for most houseless eliksni and lower class workers in Houses.
Voltesk: A shorter season usually marked with increased trade and travel.
Voldryst: A period where the cold starts to creep in and eliksni bulk up their resource stores, especially amongst the houseless and places with already cold climates.
Molts
Molts are treated as life stages, comparable to us using "child", "teenager", and "adult".
Egg Molt: Nymph stage, a newly born eliksni retains their egg molt for around 67 days. (~75 Earth days, or ~2½ Earth months)
First Molt: Child stage, from toddler-like state to something like a preteen. Molting after ~67 Riis days and lasting ~3 Riis years with shorter, less dramatic molts in that time.
Second Molt: Adolescent stage, encompassing preteen to pre-adult. The start of more dramatic changes, like setae growth, fuller mandibles, and harder chitin. The molt happens at ~3 Riis years, and they stay at this life stage with a few sparse molts every year until they're ~7 years old.
Third Molt: This molt marks biological maturity, not legal maturity (in most Houses). This molt happens when an eliksni is between 7 or 8 Riis years old, and at this point they are their natural adult size (though some may have a few smaller molts that add to their size).
Eliksni can have future dramatic molts due to ether intake or triggering certain hormones to cause a sex change (I subscribe to @ahamkara-apologist's headcanons regarding that), but it can become more difficult with age. Usually, an eliksni will stop future molts when they get past 120 Riis years in age.
Life Events
[I'm going to just share this as my bullet notes lay them out. Years in this section are only in relation to Riis]
0-2: baby. spending most of the time swaddled to parents.
2-3: learns to walk on two legs rather than crawling on sixes.
3-4: begins getting socialized with unrelated peers. family trade tutoring.
4-6: basic schooling or further tutoring.
6: finds a mentor and begins apprenticeship
7-8: possible early graduation or entering higher academic classes
9: biological maturity
10: socially/legally mature
11-12: latest point of graduation for certain trades
20-30: usually expected to have at least one life partner and/or hatchlings during this period.
~70: considered "old".
~130: typical retirement point.
~150-180: typical period for an eliksni to die of age or illness.
