Gamma rises as expiration approaches, and for a same-day option that peak arrives in the final hour. So the 0DTE gamma feedback loop is at its most intense from roughly 3 p.m. to the close — the “power hour” where the gamma effect dominates.

What intensifies

With gamma peaking, dealer hedging per unit of price move is at its largest, so whatever the regime is doing, it does it harder into the close. In positive gamma, pins tighten — price gets magnetized to big strikes and ranges compress. In negative gamma, breaks accelerate — the last hour can produce the day's fastest, most violent move.

The last hour doesn't invent a new regime — it turns up the volume on the one you're already in. Peak gamma, peak effect.

The two faces of power hour

Know which you're in. A pinned, positive-gamma close means fade the edges toward the magnet strike and distrust breakouts. A negative-gamma close means respect momentum and expect extension — the exact wrong time to fade. Misreading the regime in the final hour, when the effect is strongest, is where a calm day's small loss becomes a large one.

The practical cut

Two more realities of this window: spreads widen as market makers de-risk, and any in-the-money 0DTE you hold marches toward auto-exercise. Many scalpers are flat before the worst of it. If you do trade the power hour, trade it knowing the gamma effect is amplifying everything — and let the live dealer map tell you which direction it's amplifying.