The window opens at month 9 and peaks in the quarter ending month 21, then decays monotonically. Half of all companies that ever raise a B have closed by month 24. Median time-to-B among companies that make it within three years has barely moved: 18.5 → 18.3 → 17.2 months across three eras.
What collapsed is how many make it, not how long it takes those who do. Only about 30% of companies that raise an A-scale round ever raise a genuinely larger follow-on — 23% under a strict definition, 39% under a loose one. Measured from SEC Form D filings, 2014–2026.
Every claim above comes from work LeanScale published. These are the sources.