There is no fixed schedule to replace tranny fluid on CX9. (Same tranny as Lexus/Toyota's)
You replace the fluid when something does not feel right (according to Mazda).
Or, the fluid gets too dirty during full-circle inspection of Mazda.
Anyway, I personally do not buy that. I learned my lesson from BMW's life-time tranny fluid (what a joke!).
There is a thread on this, and lots of debates also.
I keep 30K schedule on the tranny fluid (if flushing it).
If drain and replace (i.e. DIY), do it at 30K/15K/15K...
My personal view of course. I am sure someone would disagree. To each one's own.