In an isolated SMPS feedback design, how could optocoupler latency be higher than the switching period?
Note that the opto-coupler is powered by the DC after all the filtering components, so the feedback delay will be much slower.  The operation of the supply will have a parameter of "Load Response", "Load Regulation" (or something similar) that lists the typical response to a sudden load change, (time wise this is likely in the range of several mS).  The extra (or missing) switching pulses generated during this response time will be well filtered by time they reach the DC output.  So the "latency" in uS is not very critical in this case.