I was trying to determine if someone passing close by was the person I thought they were. ( They were! )
Annoyingly, the Strava time axis can only be Elapsed Time, not time-of-day.
So I had to zoom in on the map to the fly-by point, establish my elapsed time, add it to my start time to get the time-of-day.
Then repeat with their activity, and see if they matched.
Clumsy.