Hi there,
I see you're trying to steal my customers
... nah, I was just kidding
Good luck with your implementation, maybe I will try Python myself at some point.
I just wanted to let you know how I calculate the time stamp. I just released a new beta version that updates the metadata, I hope that it works on all time zones. I'm waiting feedback on this.
First I set the modified date to local date and time, then I extract the UTC (Coordinated Universal Time) date from this local date and write it in the xml file.
Then I calculate the offset between UTC and local time, in minutes, and multiply this with -1. I write the result in the tz attribute.