The code will currently show the local timezone of the user for all events. Just in case this doesn't work, it would be good to have a dropdown that shows (1) the default timezone, which will hopefully work in most cases; and (2) once a new timezone is selected, reload the events in that timezone.
https://github.com/qubeshub/hubzero-cms/blob/ca2647b110d377e24a21c72852a3475c71830657/app/plugins/content/formathtml/macros/group/events.php
The code will currently show the local timezone of the user for all events. Just in case this doesn't work, it would be good to have a dropdown that shows (1) the default timezone, which will hopefully work in most cases; and (2) once a new timezone is selected, reload the events in that timezone.