Stan,
According to the Space-X video here:
https://www.spacex.com/launches/mission/?missionId=transporter14
The second stage de-orbit burn occurred over north Africa starting at T+2:40:16 and it lasted a few seconds. Launch was at 21:25:00 UTC so that means that the burn was over by 00:06 UTC, before we saw the stage come over the UK. Three minutes later it deployed a re-entry demonstrator called Mission Possible and then started the passivation with thruster firings and venting residual propellant which is what we saw.
I have video from my SE pointing camera (UK004E) showing the stage rising out of the Earth’s shadow in the SSE with with the venting starting around 00:11:46 UTC.
