False — with one real exception.
Movement at the London open is bigger in only 2 of 19 markets. EUR/USD — the pair the claim is usually made about — moves 90% of its normal size in its own open hour. The exception is GER40 at 123%, which is no coincidence: that hour is also the Frankfurt cash open.
| Market | In the window | Rest | z | Movement | Samples |
|---|---|---|---|---|---|
| Silver (XAG/USD) | 48.0% | 50.3% | -4.2 | 108% of normal | 10,393 |
| EUR/USD | 50.6% | 48.7% | 3.7 | 90% of normal | 11,804 |
| USD/CHF | 47.9% | 50.5% | -3.6 | 108% of normal | 6,446 |
| EUR/JPY | 51.3% | 49.9% | 2.7 | 104% of normal | 10,450 |
| GER40 (DAX) | 50.1% | 51.7% | -2.2 | 123% of normal | 5,400 |
| USD/CAD | 50.9% | 50.1% | 1.5 | 84% of normal | 11,836 |
Every claim here reduces to a window on the clock or the calendar, so it can simply be checked. We compare the claimed window against the rest of the week on 23 years of hourly data across 19 markets, measuring two separate things the folklore tends to conflate: direction (does the window close higher more often?) via a two-proportion z-test, and movement (is the average move bigger or smaller?). A window can be perfectly ordinary in direction and genuinely quieter in movement — saying which is the entire point.
The bar here is |z| ≥ 2, deliberately more lenient than the |z| ≥ 3 this site applies to its own numbers: when testing someone else's claim, failing to reject it even at a lenient bar is the stronger statement.