This study aims to investigates the nucleation and growth mechanisms of gold nanoparticles (GNPs) and gold nanostars (GNSs) using time-resolved in situ small-angle X-ray scattering (SAXS) at the ESRF beamline ID02. By employing an accelerated Turkevich method, HAuCl₄ is rapidly reduced in an acidified ascorbic acid solution, forming GNPs. The addition of AgNO₃ within the first few seconds promotes nanostar morphology through silver-gold interaction. We focus on how temperature and the precise timing of AgNO₃ addition influence particle size, shape, and concentration. This research aims to uncover key mechanisms in nanoparticle formation and improve control over GNS synthesis for catalysis, sensing, and biomedical applications.