Abstract--The provision of Quality of Service in Grid environments is still an open issue that needs attention from the research community. One way of contributing to the provision QoS in Grids is by performing meta-scheduling of jobs in advance, that is, jobs are scheduled some time before they are actually executed. In this way, the aproppriate resources will be available to run the job when needed, so that QoS requirements (i.e., deadline) are met. This paper presents two new techniques, implemented over the red-black tree data structure, to manage the idle/busy periods of resources. One of them takes into account the heterogeneity of resources when estimating the execution times of jobs. A performance evaluation using a real testbed is presented that illustrates the efficiency of this approach to meet the QoS requirements of users.