I've been long plagued by Strava's time interpretation of my GPS tracks, and come up with a generic solution.
Meet TimeShift: https://github.com/aidaho/timeshift
It's a tiny command-line utility written in Python, tasked with the shifting of a timestamp sequence
(that's what GPS tracks are: a sequence of timestamped coordinates).
A short usage example will look like this:
`python timeshift.py --format="%Y-%m-%dT%H:%M:%SZ" --time-diff="-3" track.gpx`
(that's what I use for my tracks to make them appear with correct time in Strava)
A more comprehensive help is available by running `python timeshift.py --long-help`
That's it, no more separations from the group rides.
Just thought it might be useful for someone too here.