The growth of e-commerce has increased the number of home deliveries that need to be made in retail operations. Strategies such as reducing routing distance using optimisation models have been the most popular approaches to enhancing the efficiency of the delivery process and reducing its environmental burden. However, recently, customer purchasing behaviour has become relevant in understanding demand trends and increasing the effectiveness of the supply chain process. Customers are subject to different incentives to drive them to wait longer for their home deliveries. These incentives allow companies to pool and ship in more cost-efficient and energy-friendly alternatives. In this article, we present a methodology that uses a mixed-integer-linear programming model to evaluate the impact of extending delivery slots. We use real data from one of the largest retail companies in Mexico to analyse the impact of different time slot extensions for three different criteria: distance, transport costs and CO2 emissions. Our results show that the common approach of minimising distance is not recommended for any of the scenarios under study. On average, having up to 4 days for deliveries leads to savings of 57% in total distance, 61% in total costs and 56% in fuel consumption and/or CO2 emissions.