And then there's your assumption that tini is in the USA...
Australia also has Central Time, defined as GMT +8.5 hours (some of it goes onto daylight saving in the Southern summer, some of it does not).
There are some SDK Transforms for converting GMT, if my memory serves me correctly. You can also use System(99), which returns the number of seconds since midnight GMT on 1970-01-01 and Oconv(thedate, "DZ") to return the time zone, and make some formula based upon these.
The switch to and from daylight saving is never easy, particularly in those countries that move it around for political convenience or otherwise manage it in a non-uniform fashion.