I am not sure I understand what behavior you are expecting.  But datetime.now() is documented as returning "the current local date and time" (assuming no tx= argument is provided) while datetime.utcnow() returns "the current UTC date and time".  So I would expect the two to provide a similar value only if your system/process local time zone is set to UTC.  I'm guessing the time zone in effect when your examples were run was 8 hours ahead of UTC:

>>> (1523942165.202865 - 1523913372.362377) / (60*60)
7.998011246654722

https://docs.python.org/3/library/datetime.html