The probe-window timing constraint
TikTok's per-video ranker runs three sequential gates after upload: the seed-distribution gate (0-30 minutes, ~500 viewers), the probe-expansion gate (30 min-4 hours, 500-50,000 viewers), and the broad-distribution gate (4+ hours, 50,000+). Each gate reads engagement-velocity from the previous window. A like order that starts arriving 30+ minutes after upload misses the first gate; one that starts 4+ hours after misses both early gates and only affects the broad-distribution tail, where the marginal lift is much smaller.
