Depolarization effects in (Formula presented.) -based ferroelectric devices have gained significant interest for research on non-volatile memory applications. Understanding retention mechanisms enables device optimization for temporal and brain-inspired computing in hardware. This work presents a ferroelectric capacitor stack that shows a metastable (Formula presented.) state that relaxes on a millisecond scale through a unique interface configuration. Electrical characterization demonstrates the device's capability for implementing tunable time constants in hardware, followed by investigation of the electronic mechanisms underlying observed retention times to facilitate modeling of retention processes in (Formula presented.) -based ferroelectric capacitors. Internal electric fields stabilize one polarization state, enabling unipolar operation with millisecond retention for the unstable polarization. The observed retention loss depends on both polarization state and programming conditions, allowing exploitation of multiple memory time-scales in a single device. The defective interface in the material stack provides insight into retention loss mechanisms and internal bias field origins in (Formula presented.) -based ferroelectric devices. These internal bias fields are related to interface composition, with oxygen vacancies identified as a possible source. The results demonstrate that (Formula presented.) -based ferroelectric devices offer an elegant solution for realizing tunable time constants in scaled memory devices, providing memory elements for brain-inspired temporal computing hardware.