Our research has empirically supported the long-term manifestation of the resource depletion, accumulation, and investment mechanisms which have been proposed in the conservation of resources (COR) theory but have been under-investigated in the work–life balance (WLB) literature. Specifically, we have examined how multiple work and non-work contextual demands and resources impact working mothers' WLB satisfaction and job retention via changes in their personal resources of childcare time and family finances through these three mechanisms. The use of multilevel analysis and a longitudinal design has enabled us to evaluate the effectiveness of contextual resources for WLB in consideration of both their short-term influence as transient resources via within-individual fluctuations and their long-term impact as durable resources via between-individual differences. We have tested a total of 27 hypotheses on a nationally representative British sample of 10,983 working mothers who participated in a longitudinal study over 6 years of their children's primary education. By highlighting the critical role of both childcare time and family finances in promoting working mothers' WLB satisfaction and job retention over time, our research contributes to the WLB literature that has predominantly emphasized time-based but neglected financial-based constraints and resources. We have found that working mothers may trade their childcare time for better family finances when they undertake a managerial role. Thus, becoming a manager serves as both a time-based demand and a financial-based resource for working mothers, which points to the specific rather than generic nature of contextual demands and resources.