Should Google's unit converter/calculator search feature convert time zones?

Every time I need to covert a time zone I instinctively type something like "7:30 PM MST in Arizona time" or "6 AM Iceland in San Francisco Time" and expect it work pretty much the same as typing "80 mph in m/s" or "9003 + 1834" in the search box, but it never does...<p>Is there a good reason why? Am I out of line thinking that converting time zones would work like converting units?