For Zwift, Turbo, Some Indoor Trainer rides, some treadmills, Peloton, FullGaz or other activities with a "fake" GPS track in another country:
You must select "Virtual Ride" when you use my tool to upload to Strava. What is happening is Strava is detecting the "fake" map made by your virtual ride application. Therefore, Strava is overriding the timestamps that the tool sends along.
By default, Strava will use the time zone for the map location (such as Fiji with Zwift) if you select "ride" as the activity type. If you select "Virtual Ride", Strava will use the time zone set in your profile: