Bulk metallic glasses (BMGs) are alloys characterized by a disordered atomic arrangement, achieved through rapid solidification from the melt. Because of their distinctive properties, BMGs have recently emerged as promising candidates for additive manufacturing techniques such as laser powder-bed fusion (LPBF). In this study, we conducted fast differential scanning calorimetry (FDSC) experiments to explore the crystallization process of Zr-based BMGs designed for applications in additive manufacturing. Employing a modified FDSC sample holder for quick integration into a synchrotron X-ray beam, we simultaneously measured time-temperature-transformation (TTT) diagrams and alloy diffraction patterns. Ex situ scanning electron microscopy (SEM) unveiled that sample degradation during thermal cycling remained unavoidable, despite employing an argon atmosphere. TTT diagram measurements were thus also carried out using a setup that incorporates FDSC within a vacuum chamber, allowing for an in-depth investigation of alloy degradation in situ. The findings were then correlated with the oxygen content of the alloys to optimize the additive manufacturing process.