Molecular homogeneity frequently plays a decisive role in the effective application of organically modified silicate copolymers, but direct characterization methods are not always available or convenient. We present an alternative tool for determining kinetic parameters for alkoxysilane hydrolytic copolycondensation using a semibatch reactor with varying time of injection of one component. All necessary kinetic parameters are determined from a series of ordinary Si-29 NMR data in a straightforward case study: copolymerization of dimethyldiethoxysilane and trimethylethoxysilane. As further validation of the rate coefficients, the results of a new series of experiments (varying the monomer ratio) are successfully predicted by the semibatch copolymerization model. With this model, we explore optimizing the molecular homogeneity of the copolymer products. Even for this relatively simple system, the optimal injection time is a complex function of residence time, but early injection of the faster-condensing monomer gives the best homogeneity at long residence times.