The event for which the speaker/lecture/... data is displayed is determined by its organization ID, which you set in the Wordpress admin interface. However, you can override this setting in a shortcode in order to display last year's speakers, for example. All shortcodes accept an optional org-id="..."argument, so for example
will display the speakers from the event whose id is xyz123.
timezone="Europe/Berlin" for central europe
timezone="America/New_York" for US east coast
and so on. The appropriate daylight savings time adjustment is automatically applied according to the date, you do not have to do anything special. The name of the timezone is the usual timezone database name, sometimes also called Olsen name. The complete list can be found at https://en.wikipedia.org/wiki/List_of_tz_database_time_zones.