I know when certain commits were created (at remote A, say) based on their log messages. What I don't know is when remote B fetched and merged said revision. I need it to determine when a bug crept in.
Is this possible through Git?
If this is fetch, try git reflog --date=local, see https://stackoverflow.com/a/3748722/88442 .
if it have a local merge, a git log would do.