A 3-day test misses the weekly cycle and can be off by ±2-4 points on weekday-skewed traffic.

A 3-day test misses the weekly cycle and can be off by ±2-4 points on weekday-skewed traffic.
The failure: stopping mid-week, when B2B checkout converts higher Tue-Thu. You measured a day-of-week, not a variant.
— Payday cycles and weekends shift intent too.
— Fix: run in whole-week multiples so each variant sees identical day composition. Minimum one full cycle, never partial weeks.
Read the number, not the story. [≥1 full week · ±2-4pp]