First things first: using time.time on a single run is not a good benchmark. You’re better off using built-in functions that are meant for this kind of thing. Have a look at the timeit 2 module.
Second, it is not really clear what you are comparing here. You say that things “got slower than usual” but then compare with a Macbook. So what are you comparing? Different versions of Pytorch on the macbook? Different computers altogether? Please give more information.