Maybe campaign manager is asking participants to fill the form in PM. I think it is very likely that they have a form as if you check the spreasheet you will see Timestamp column which generally by default comes when you have form linked with spreadsheets.
Also why would a campaign manager care about the time when the participant joined. I maybe wrong though. Can you post the link of the bounty so that I can also look into it.
Just found their thread and I saw they posted the link of the form publicly. So, anyone can fill that form.
Here is the form:https://docs.google.com/forms/d/e/1FAIpQLSfcR1SjFmtA8X8qgmtqbqHlVq-aCkFU8gnYHUGO1VHExlSdwA/viewform