Free Electron Lasers deliver intense, tunable, ultrashort X-ray pulses that allow the investigation of transient dynamics in a wide range of systems. However, short- and long-term variations in the pulse arrival time limits the attainable time resolution. Correcting for this requires non-invasive and accurate shot-by-shot time delay information. Established transient reflectivity cannot be used with low intensity monochromatic radiation. We aim to achieve this using non-resonant X-ray-induced THz emission from a spintronic device.