A vehicle routing problem with synchronization constraints arises in urban freight transportation, in which context customers require deliveries from one or more logistics service providers. These deliveries should be efficient to reduce idle times at the delivery locations. Idle time is defined as nonservice time between the first and the last delivery received by the customer. We propose a strategy which relies on self-imposed time windows, and we compare our approach with an exact determination of a feasible schedule and fixed time windows. The results show that idle times can be reduced by 54.12%-79.77%, with an average cost rise of 9.87%. In addition, self-imposed time windows provide solutions with 15.74%-21.43% lower costs than feasibility checks for short runtimes and 13.71%-21.15% lower than fixed time windows.