You can check the docs to understand the functionality of those parameters:
timeit is a magic function to extensively test a given block of code.
-n 1 means that run the given block of code only once, and
-r 10 means that repeat this experiment of measuring time 10 times and get the best result out of it.
Each time you run the command, the time will differ slightly. It’s mainly because of how your OS handles multi-processing, that is, how it allocates/prioritizes time chunks for each process running under the OS.