In response to ensuring the rapid opening and post-opening life of existing traffic lines rehabilitation, ultra-high performance concrete (UHPC) was developed with sufficient construction time and super-early-strength (reaching open strength within several hours). Based on the UHPC mixture proportion designed via maximum compactness theory, the effect of the substitution rate of ordinary Portland cement (OPC) on the mechanical performance and workability of sulphoaluminate-ordinary Portland cement system (SAC-OPC system) concrete was studied via experiments, and the OPC substitution rate was determined. Super-early-strength UHPC with initial setting time of 36 min and 3 h compressive/flexural strength of 414/170 MPa and super-early-strength UHPC with initial setting time of 40 min and 3 h compressive/flexural strength of 362/13.9 MPa are prepared via the orthogonal tests on the mechanical performance and workability of SAC-OPC system concrete with early strength agents (lithium sulphate, aluminum sulphate), enhancing agents (nano calcium carbonate) and slow-setting agents (slow-setting powder, sodium tetraborate). The mechanism for the performance formation of super-early-strength UHPC with sufficient construction time was studies by SEM and XRD. The results show that, with the increase of OPC substitution rate, the setting time of UHPC decreases first and then increases, the slump extension continues to increase, and the mechanical performance of UHPC generally shows a decreasing trend in the early stage and an increasing trend in the later stage. The super-early-strength and prolonged initial setting time are mainly due to the cumulative effect of the synergistic hydration and early strength agents, enhancing agents, and slow-setting agents.