Theta — time decay — is not linear on a 0DTE option. It's slow in the morning and accelerates through the afternoon, falling off a cliff into the final hour as the option's remaining time value collapses toward zero at expiration. That acceleration is why holding a winner “for a little more” late in the day so often backfires.
Why the decay speeds up
Time value is largest when there's the most time and uncertainty left, and it drains fastest when there's least. By mid-afternoon, a 0DTE option's extrinsic value is evaporating quickly regardless of direction — so an at-the-money option that isn't moving decisively in your favor is losing value every minute just from the clock. The cliff is steepest in the last hour, where the option becomes almost pure intrinsic value or nothing.
In the morning, time is cheap. By 3pm, the clock is charging by the minute — and it doesn't care that you're right on direction.
The exit rule
Bank 0DTE winners before the cliff gets steep — many scalpers are done, or at least taking most off, by early afternoon rather than pressing into the theta acceleration. If you do hold a runner into the afternoon (a strong trend), keep a tight trail, because the decay is now a headwind on top of any reversal risk. Don't let a green option turn red because you were waiting on a move the clock outran.
How it fits the exit ladder
This is why scaling out matters so much on 0DTE: you bank pieces while time value is still there rather than betting the whole position on a late move against an accelerating clock. NoVo's exit ladder is built around this reality — taking profit at levels and trailing the runner — so the theta cliff works for your discipline instead of against your patience.