no problem.
They said nothing about season being there for longer - It’ll most likely rotate as it was Mid season when Darkmoon faire came out, and the Darkmoon races was when a quarter was left - meaning it’ll rotate still same time as Arena as they said.
Arena/Duel are suppose to be in sync on rotation as that when they update the card pack they reward since they share the same system for reward and use the 12/3 system.