Better method of a timer in Python
If the goal is to run a task at the same time each day, it is better
to capture the value of the real-time clock, because using successive 24 
hour intervals can give you a "time creep".  Something along these lines 
would work fine (you'd probably put this in a separate thread):

import time

def time_of_day:
     return time.strftime("%H:%M:%S")

target_time = "18:00:00"

while True:
    while time_of_day() != target_time:
         time.sleep(.1)
    call_function()
    while time_of_day() == target_time:
         time.sleep(.1)