Nowadays, Operating Rooms (ORs) scheduling and planning represent one of the most challenging aspects in healthcare systems management. In particular, one of the main concern is doubtless the under-use of the surgery rooms, that one can tackle by modelling different management decision aspects. The number of ORs available in the operating theatre and their daily opening time, the ideal OR Utilization Rate (UR) that the hospital aims to fulfil, the possibility to transfer patients between different surgical units (SUs) are just some of them. Taking into account these management and economic factors, we develop a multi-criteria integer linear optimization model for the advance scheduling of patients for the Azienda Ospedaliera - Universitaria Policlinico Umberto I of Rome, among the largest public hospitals in Europe for by total area occupied. The problem is formulated according to an open scheduling strategy that, for each surgical case placed on a waiting list, determines the date, time, and operating room resources needed. Extensive tests were carried out on real data collected during twelve weeks in two SUs, each of them consisting of two ORs. The aim of the study is to evaluate the impact of different policies of opening times on the hospital Key Performance Indicators (KPIs) of interest. The results show a relevant improvement of the ORs usage of the case study.