This paper introduces the idea of unified unit commitment and economic dispatch modeling within a unique tool that performs economic dispatch with up to 24-hour look-ahead capability. The tool provides financially binding dispatch and ex-ante locational marginal prices (LMPs) for the next 5-min interval and advisory commitment, dispatch schedule and prices for the remaining scheduling horizon. Variable time resolution and variable modeling complexity are used in order to reduce computational requirements. A finer time resolution and detailed modeling are used during the first hours of the scheduling horizon while coarser time resolution and simplified modeling during the last ones. The viability of the method for medium-sized systems is demonstrated through its application to the Greek power system.