The quest to optimize the performance of cadmium oxide (CdO) nanoparticles has led to an investigation into how varying reaction times during synthesis impact their properties. By employing a systematic wet chemical synthesis method, the reaction time was varied while keeping other synthesis parameters constant to observe their influence on the properties of the nanoparticles. Using a combination of characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy, the changes in crystal structure, particle morphology, optical absorption, and electronic behavior associated with different reaction durations were analyzed. Shorter reaction times spanning 30–60 min tended to produce smaller particles with a more uniform size distribution, while longer reaction times spanning 90–120 min resulted in larger, more defined, and regularly shaped particles. The crystallite size increased from approximately 18.03 nm at 30 min to about 23.67 nm at 120 min. These changes correlate with variations in optical absorbance, as depicted via a Tauc plot, which shows energy bandgaps ranging approximately 2.5 eV for nanoparticles synthesized for 60 min and 1.7 eV for 120 min. Notably, this study demonstrates how tailored reaction times can fine-tune the bandgap and carrier concentration of CdO nanoparticles, which are critical factors for their performance in various technological applications. The results of this investigation offer a deeper understanding of the interplay between synthesis conditions and nanoparticle properties, paving the way for the design of advanced materials with tailored characteristics for next-generation technological applications.