Odour emissions from dairy manure composting pose a significant challenge to sustainable manure management. This study evaluated soybean peroxidase (SBP) (combined with calcium peroxide (CaO2)) as an odour-mitigation strategy and examined whether application timing influenced treatment performance during 56 d of dairy manure composting. Three treatments were compared: control, split-dose SBP application, and single initial SBP application. The physicochemical properties, ammonia (NH3) levels, sulphur compounds, volatile organic compounds (VOCs), volatile fatty acids (VFAs), odour intensity, and bacterial community succession were monitored, and exploratory correlation analysis was used to assess the associations among environmental variables, odourants, and dominant taxa. The results showed that SBP increased organic matter decomposition, and the single-dose treatment had a higher final total nitrogen content than the control. SBP altered early compost chemistry and bacterial succession, with the single-dose treatment showing the clearest response. This treatment produced the largest reductions in cumulative NH3 (19.2%) and phenol (31.6%) emissions relative to the control and was associated with a lower early stage pH value. The mean odour intensity over 56 d was 11.7% and 15.3% lower under split-dose and single-dose application, respectively. In contrast, sulphur compound emissions did not differ significantly among treatments, and total VFA emissions were not reduced. Overall, the results indicate that an early single-dose application of SBP is more effective than a split application for mitigating selected odourants during dairy manure composting. Emissions are expressed per unit of initial volatile solids. As a benchscale source characterization, these findings require field-scale validation in the future.