In the General tab of Tools > Setup, find the Location Settings section. In the Time Zone field, change select the time zone where your HomeTroller Zee S2 or SEL is installed. The time zones are sorted by country alphabetically.
For accurate sunset and sunrise times, you will want to select the location nearest to you in the Location drop-down menu. This is also sorted alphabetically by country, and you have the option of manually entering your latitude and longitude coordinates if you so choose.