I just thought that the memory card in my C1 pro has died or something, as newest file on the card was 10 days old. Could not watch any videos on my phone (i got connection, but then it crashed and could not see the camera anymore), so i got the card out and tried with computer. Newest timestamp said 22.2.2019 and i was just trying to see a clip from this morning (4.3.2019). I found the video i wanted, it just showed that 10 days old timestamp instead of today.
So +1 for gps as time source, its just stupid not to use it when it is available. Many products have gps-chips only for time, so what have the coders been thinking when something else could replace reality?