The ONLY thing you have to do is include in /boot/config.txt:
DO NOT fiddle with the software or attempt to manually synchronise - it all happens AUTOMATICALLY.
If you need to set the RTC initially (if NTP not available) you can use hwclock --set see man hwclock for details.
1) Your service is terminated (all process started by this service are killed) when your last script (python here) execution is finished.
Execute the python script into a terminal, your script exit with default value of 0 (process exit success code) after python file execution because you have not a forever loop (while). Service file is principaly for ...
After modifying wpa_supplicant.conf you need to make wpa_supplicant re-read the configuration file.
wpa_cli -i wlan0 reconfigure
(assuming wlan0 is your wifi to reconfigure)
reference - wpa_cli man page
I upgraded my Raspberry Pi to Stretch and I was unable to have any success with any variation of the net.ipv6.conf.all.disable_ipv6=1 answers.
Manually running sudo dhclient -4 -v eth0 to get my network/internet connectivity back worked, however as stated by the original poster it does not survive a reboot.
I noticed that sudo ifup -v eth0 called dhclient,...