The peak period for public speaking anxiety occurs approximately 30 seconds before beginning and during the first minute of speaking.
"Commencing is the part—the point where people are most nervous about speaking is about 30 seconds before and about a minute into what they're doing." (said at 2:19:10)
No biomedical literature indexed in PubMed directly evaluating the specific timing claim (peak anxiety occurring approximately 30 seconds before beginning and during the first minute of speech onset) was located. While classic communication studies often describe speech anxiety 'milestones' (anticipation immediately preceding speech and confrontation during the first minute), this specific quantitative window could not be verified in the searched databases.