We investigate a vehicle routing problem in which customer requests are either known in advance with respect to the planning of the distribution, or they arrive online during the distribution process. Each request is associated with a time window. The company managing the distribution has a given fleet of vehicles to serve the customers, and, in addition, occasional drivers are available to perform the service, i.e., private citizens who are willing to distribute some customer orders in exchange for a compensation. Each occasional driver specifies the time window in which he/she is available. A penalty is incurred when violating time windows as well as when a request is not served. The objective of the company is to determine the distribution plan that minimises the distribution cost, which is given by the sum of the cost of regular vehicles, the compensation paid to the occasional drivers and the penalty cost.