Our team was unable to find any built-in functions for handling timezones/offsets and had to develop our own library that uses the built-in timezone database installed on our Redhat servers.

Check out this article: Time Zones and Offsets and ObjectScript, Oh My! | InterSystems Developer

Here's the related library: tz---ObjectScript-Time-Zone-Conversion-Library

Let me know if you have any questions/problems with this library.