Here’s a link to the real-time video clip from UK004E. The cloud starts in northern Capricornus and then moves up into Aquila. You can see a number of the deployed spacecraft ahead of the cloud and a brighter object in the cloud. The brightest dot, towards the end, is the venting second stage itself. Mel’s video linked above shows the individual events in far higher resolution and I assume that the significant brightening of the second stage around 00:12:45 is the large venting event shown on Mel’s video.
https://nickdjames.com/Spacecraft/20250524_propvent/UK004E_20250624_001126_ndj.mp4
The final spacecraft deployment was the Mission Possible re-entry experiment at T+2:43:53 which is just before 00:09 UTC and the first sign of the cloud is at around 00:11:30 so only around 2.5 mins later.