The hardest part of trading 0DTE and 1DTE options isn't finding the setup — it's the fill. A short-dated SPY option is a fast, twitchy, thinly-quoted instrument, and the gap between clicking and executing is where the trade is won or lost.

Speed vs the spread

You face a dilemma on every entry. A market order guarantees a fill but pays the full spread and can walk through a thin book. A limit order controls your price but may never fill as the option runs away from you. On short-dated contracts, both failure modes are expensive — overpay, or miss the move entirely.

Gamma makes it worse

Near expiration, gamma is high: the option's delta — and therefore its price — moves fast as SPY moves. That means the "right" limit price is a moving target. By the time a slow, manual decision reaches the book, the quote has already changed. Human reaction time is a tax you pay on every short-dated entry.

On 0DTE, you're not just betting on direction. You're racing the spread and the clock to a fill that still makes the trade worth it.

What actually helps

The human tax is smallest when the decision was already made: a level you chose in advance, a size you fixed before the session, and a price you are willing to walk away from. That is why the fill problem is really a preparation problem — and why a structural read made before the tape gets there is worth more than a faster finger.