In the High Rainfall Zone (HRZ) of southern Australia, long-season winter canola types have been commercially available only since 2011. Experiments in this region show that these varieties can provide improvements in grain yield over spring types of >20% because of their ability to make better use of the longer growing season. However, within this longer crop duration, the optimum length and timings of the critical growth phases to maximise grain production are unknown. Data from eight field experiments conducted between 2010 and 2014 at Hamilton, in the HRZ of south-western Victoria, were analysed to determine whether different phases within the crop’s life cycle vary in their contribution to grain yield and, if so, how this is influenced by climatic conditions. The dataset provided 536 genotype–environment–management combinations including 60 varieties ranging in total crop duration from 186 to 236 days. Over the 5 years, seasons were highly variable with annual rainfall ranging between 479 and 981 mm and spring rainfall (September–November) between 84 and 199 mm. The range of crop maturity types (i.e. winter and spring types) and environmental conditions provided a wide spread in growth, development and grain yield. The analysis showed a positive association between longer duration from flowering to maturity and grain yield, and showed that the duration was influenced by both environmental and genetic factors. Pre-flowering reserves made an important contribution to grain yield, and remobilisation of reserves from the pre-flowering period was greatest for winter types, presumably due to less favourable conditions for growth during grain-filling. Optimising flowering to produce sufficient pre-flowering reserves for remobilisation while ensuring that environmental conditions post-flowering are such that the grain-filling duration is maximised may provide a strategy to increase yields in this environment.