Time-multiplexed interconnect structures, timing optimization techniques and software tools for said structures, for programmable semiconductor ICs is disclosed. A first aspect is a programmable logic device, wherein a plurality of outputs from logic blocks is coupled to a plurality of inputs to logic blocks by a single wire segment comprising a programmable time multiplexing method. A second aspect is a software placement and route tool, wherein a plurality of routs is assigned to a single route, wherein the plurality of routs is routed in the single route by a time multiplexed method. A third aspect is a critical signal propagation path in a programmable logic device comprising global non-overlapping control signals and time multiplexed wires, wherein each control signal assigns a programmable time slot for multiple signals within one of said wires, further comprising one or more critical signals assigned to the last multiplexed time slot.