For systems without battery clocks, which I think are all GL iNet travel routers, they seem to use the last time stamp in /etc. I have some GL-AR300M running as servers in restricted areas, so I reboot them nightly with the cron entry:
18 0 * * * sleep 70 && touch /etc/banner && sync && sleep 5 && reboot
This way the initial time set on boot is after the time the cron entry would run, to make sure I do not get into a boot loop. I have used logread to verify that the time on boot is set to the time stamp on /etc/banner and then changes once the system starts talking to the NTP servers. This work-around came from the post:
For how long this takes on your system, look for a time jump in logread after the system boots. It normally happens around when hostapd: attaches to your AP.