There pretty much is. They have stuck to a 3 month window (+/- a week or 2) for the a large chunk of the past several seasons. Exact times laid out would be nice, be we have seen how people react if they need to change it.
TBH, 3 months is the sweet spot.
They have have a few seasons 4-6 months long and the pretty much drag. Game is pretty dead after 2 weeks. Tacking on a longer break is useless.
The couple of times they have had a season shorter than 3 months, it was too short for that smaller group of players that does play beyond the first 2 weeks.
Simple solution for those who want to play other games and 3 months is too short: Play every other season. They can also simply cherry pick the Themes they like, and skip the ones they don’t like.