Yes, that's true, instructions generally take more than one cycle to execute, although the most common ones are fast. But processors these days can execute more than one instruction at a time (this has nothing to do with multiple cores, this is on a single core) and aren't bound to the order the instructions appear in the code, it will make sure that instructions that are dependent on each other will be executed in the right order, otherwise it can opportunistically execute whatever it has room for. Modern processors even speculatively executes code from branches it doesn't yet know will be taken, which caused the whole Meltdown/Spectre security headache.