I made a very small app which is generating a GPX for a 30 minute activity. (I am doing this because I do not have a waterproof device to track my swim)
I can upload it and the activity looks just like I intended.
Except one thing. It moved to 3 hours later. So when I upload it, all the times from the GPX file look like this: 2021-08-29T13:20:45Z .
I have nothing in the timestamps outside of the 13:20 - 14:05 interval. Why does the Strava Activity say this: 4:20 PM on Sunday, August 29 instead?
The wikipedia article about the GPX format states:
Dates and times are not local time, but instead are Coordinated Universal Time (UTC) using ISO 8601 format.1
Your local time probably experiences a 3 hour time difference to UTC