Abstract: Within a cooperative context, this study focuses on the establishment of a collaborative and mutually beneficial delivery ecosystem. Considering a dual-layer service supply chain composed of an instant retail platform and third-party logistics providers, the paper introduces user time sensitivity as a factor to develop three collaborative delivery strategy models: no cost-sharing by the platform, fixed-proportion cost-sharing by the platform, Nash-based cost-sharing by the platform. The impact of cost-sharing and bargaining on collaborative relationships is analyzed by comparing the performance of different strategies. It is revealed that the adoption of cost-sharing strategies enhances overall profit and service levels, with the Nash-based cost-sharing strategy achieving superior results compared to the fixed-proportion one. However, both strategies amplify the double marginalization effect in the supply chain due to increases in selling prices and service contract prices. Through an analysis of bargaining power, it is found that the Nash-based cost-sharing strategy does not always positively impact the benefits of instant retail platforms; when platform bargaining power is low, its profit may be lower than that of a no cost-sharing model. Additionally, high user time sensitivity motivates service level improvement and increases platform cost-sharing proportion while inhibiting the positive effect of Nash-based bargaining on cost-sharing.