The documentation for both $time.timezone and $time.until (https://docs.streamelements.com/chatbot/variables/time) states that they will error if no timezone is provided. This is not the case. They instead simply default to UTC.
The $time.until command does not provide an example of how to provide a timezone.
This is assuming that the parameters portion is correct and accepts a timezone rather than the summary portion which states it is always a UTC timestamp. If it does not then being able to accept a timezone would be very useful, particularly with daylight savings in mind.