gistfile1.py

from datetime import datetime                                  
from timeit import Timer                                    
                                                       
def verbose_f():                                                   
    now = datetime.now()                                             
    new_dt = datetime(now.year, now.month, now.day, now.hour, now.minute, now.second, now.microsecond, now.tzinfo)

def terse_f():                                                   
    now = datetime.now()                                             
    new_dt = datetime.combine(now.date(), now.time())

verbose_t = Timer("verbose_f()", "from __main__ import verbose_f")
terse_t = Timer("terse_f()", "from __main__ import terse_f")    

reps = 1000*1000                                                
print("verbose: %s" % (1000*verbose_t.timeit(number=reps)/reps))                                 
print("terse:    %s" % (1000*terse_t.timeit(number=reps)/reps))