I am very much impressed with some of the suggestions.
i myself am looking after the performance management systems. first of all you need to select a method of assess the performance of the employees, depending of the technique, nature of business and number of employees, you will be able to strategize Timeframes to develop the whole system.
If you are using MBOs for performance assessment then you conduct performance reviews quaterly,semi annually or annually, if you are using KPI based performance management systems, you will be need to develop performance measures for every department, line and sub-ordinates keeping the wholistic goal of organization in light. You need to have an authentic support document from where you will get feedback of performance every month.
you will also need to quantify your measure and design calculation steps to measure them in terms of %age or numbers.
after the whole development activity you need to communicate of how this thing will work, and execute.
now every month you will get those numbers as identified in the indicators, from every line manager and HoDs, which will help you assess there performance against the measures you have developed, which will later help you identify their competencies, areas of strength, and their weakness, and keeping this in mind you can also devise a Training plan for them, and process rewards, recognition, promotion, termination etc.