Not sure, how this is called. But I guess it would be good to have it called from a config file.
Eg have all the timezones in a file and use that to drive the drop down and the calculations.
I am not a program person, I just bolt things together and hope they work (adding red wine seems to help a lot)
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I tried to change the +12 to +16in the config. php file but that did not work it goes back to +12.
H.