The demand for increasingly larger quantities of locally available waste materials has led the cement industry to move away from conventional Supplementary Cementitious Materials (SCMs) and focus on other waste materials, such as recycled soda lime glass. It does not only contribute to lowering the CO2 footprint of cement, mortar and concrete, but also improves the late performance of composite blends due to its pozzolanic activity. Concerns associated with its use include increased alkali content and slow strength development at early ages. Certain activators can compensate for this behaviour, but their role in the overall hydration of the system remains to be fully clarified. In this study, sodium thiosulfate was selected as an accelerator with the aim of understanding the performance enhancement of cement-glass mixtures. The hydration of activated and non-activated mixtures was followed using isothermal calorimetry, X-ray diffraction, and thermal analysis. The compressive strengths of standard mortars were also evaluated. It was found that the values of the activated systems after 1 day were significantly better than for the non-activated system.