I would assume the season length could be adjusted over time based on player feedback as well? For example, maybe the "optimal" length is something like 10 days (hypothetical example).
Or perhaps player actions in-game could influence the seasons to change more slowly or more rapidly. For example, maybe a particular node that has been highly developed is particularly optimized for harvesting autumn resources... perhaps the citizens of that node could take part in some sort of ritual to extend autumn, but it gets more expensive the longer autumn is extended. This could also drive animosity between that node's owner and the owner of a node who was prepping to maximize the coming winter increasing opportunity for conflict.
We always want to take player feedback into account. While we hope to get most of this ironed out during testing phases, there will be things that get adjusted over time.
To your other point, yes, part of the triggers for seasonal change in Ashes of Creation won't be just time. Seasons may change more slowly or rapidly due to player action (or inaction 😎).
Timestamp to this part of the conversation, from the May 2022 Development Update.