2021.01.04 15:45:13 (1346105406892822532) from Daniel J. Bernstein:
Featured in today's edition of "See how country X is _not_ doing what the successful countries are doing": https://www.citizensinformation.ie/en/health/covid19/contact_tracing.html says that X traces contacts of an infected person P back 48 hours. Maybe finds infections caused by P, but won't find the moment that P was infected.