We describe the development of a mirror based x-ray split and delay system (XRSD) for soft x-rays at the Linac Coherent Light Source (LCLS) free electron laser at the SLAC National Accelerator Laboratory. The XRSD will add x-ray pump/x-ray probe capability to the AMO and SXR soft X-ray beamlines, allowing experiments expected to have an impact on basic energy sciences research in areas such as atomic and molecular science, chemical physics, nanoscience, ultrafast science, and imaging