Time-based exit

Definition

A time-based exit closes a position when a clock or calendar condition is met, regardless of P&L: maximum holding period, a fixed days-to-expiration threshold (the options “close at 21 DTE” convention), or an event boundary (flat before earnings). Its premise: a thesis is a claim about a WINDOW — if the expected behavior hasn’t materialized in its window, the thesis is stale and the position is unpriced risk, not patience.

How it works / structure

• Forms (engine-executable): max holding period (bars/days); DTE floor for options (exit when DTE < N — steps off the gamma cliff, greek-gamma, while keeping most captured theta, greek-theta); event boundary (exit before a named event — lens-event-catalyst window discipline); session boundary (flat-by-close — the defining rule of strategy-day-trading-styles).
• Why it exists: mean-reversion and event theses are time-bounded by construction; short premium’s risk/reward degrades as expiry approaches; capital occupancy is a cost (a stale position blocks a live one).
• Parameters: the clock (entry-relative vs calendar), the threshold, and interaction order with other exits (which rule wins when several trigger — the engine requires an explicit precedence).

When it applies

Every strategy on the platform carries one, explicitly or by expiry: reversion trades (the mean either arrived or the thesis failed), event structures (the catalyst passed), short premium (the DTE floor), intraday styles (the close). The only genuine exception is open-ended buy-and-hold, where “no time exit” is itself the declared parameter (strategy-buy-and-hold).

Risk profile & failure modes

• Clock too short: exits systematically ahead of the move’s arrival window convert a sound thesis into a friction pump — the window must come from the thesis’s mechanism, not impatience.
• Calendar clustering: popular conventions (21 DTE, month- end) concentrate flows at the same timestamps; execution quality degrades exactly on the convention (ms-slippage-friction).
• Override temptation: “it’s about to work” at the deadline is the disposition effect wearing a watch (bias-disposition-effect); the engine executes the clock.
• Wrong precedence: a time exit that fires before a stop in a fast market can exit at a worse price than the stop would have — precedence rules are part of the strategy, not plumbing.

Evidence & limits

The gamma/theta timing logic for options DTE floors is structural (Greeks arithmetic, OCC mechanics); the popular specific thresholds (21 DTE) are practitioner-published, not peer-reviewed — the platform treats the threshold as a replay-tunable parameter, the mechanism as sound. For directional trades, time exits are thesis hygiene: no external study needed to justify closing a position whose stated window expired.

Falsifiable-thesis examples

Illustrations only, not signals:

• “Adding a 21-DTE exit to this short-premium program improves its replay return per unit of tail risk this quarter” — falsified by the paired replay.
• “X will reach its target within 15 sessions” — the time exit IS the falsifier’s enforcement: at session 15 the claim is settled either way.

Cross-references

• Exit siblings and precedence partners: mgmt-stop-loss, mgmt-profit-target, mgmt-hold-to-expiry
• The options clock: greek-theta, greek-gamma, theta decay curves (glossary)
• Window discipline sources: lens-event-catalyst, qualitative-analysis (falsifier windows)