That's still a bit risky as Arizona might just change its time zone definition on a whim. I'm an engineer on one of the big calendaring applications, and it's mind-boggling how often stuff like this happens world-wide, sometimes short-notice (a few weeks in advance). It regularly gives us headaches.
Agreed, watching the rate of changes to timezone databases will rapidly disabuse you of the notion of any constant. It's rare that a day goes by without an update to some definition somewhere, which is astounding.
It might be instructive for PHBs to have a 'hasatimezonechanged.com' website counting the days since the last timezone DB change...