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We develop a geometric framework in which physical time is represented as a complex variable T=t−iτ. The imaginary component τ encodes the attenuation of coherence, while the real component t retains its usual causal role. Motivated by recent delayed-choice implementations [1–4], we show that the experimental configuration acts as an internal rotation θ of the complex time, modifying the imaginary-time difference between interferometric paths and therefore the visibility. This mechanism alters coherence without affecting causal evolution in t and does not require retrocausality. The model remains fully compatible with standard quantum mechanics, preserving unitary evolution, the Born rule, and completely positive trace-preserving maps. It provides a minimal geometric reparametrisation of the dynamical phase and yields experimentally testable predictions for visibility and temporal correlations.